Abstract
Hydrothermal carbonization (HTC) has been regarded as a promising technique for turning wet biomass into hydrochar due to its low energy consumption, low exhaust gas emissions, etc. In addition, hydrochar is an important source of dissolved organic matter (DOM), which plays a crucial part in the migration and destiny of pollutants in the environmental medium. However, there are limited studies that focus on the factors that influence the formation of DOM in hydrochar, such as hydrothermal temperature. Therefore, the current study comprehensively characterized the optical properties of DOM within hydrochar derived from sawdust (HDOM) under different hydrothermal temperatures (150–300 °C) by Ultraviolet–visible (UV–Vis) and fluorescence spectroscopy, as well as its complexation characteristic with Cu(II). The findings revealed that the organic carbon content of HDOM reached a peak of 37.3 mg L−1 when the temperature rose to 240 °C and then decreased as the temperature increased. UV–Vis spectroscopy analysis showed that the absorption capacity of HDOM at 275 nm increases with temperature and reaches a maximum value at 240 °C, indicating that high temperature promotes the formation of monocyclic aromatic compounds. High temperature enhances the aromaticity, hydrophobicity, and humification degree of HDOM, thus improving its stability and aromaticity. The E3/E4 ratios are all greater than 3.5, confirming that the main component of HDOM is fulvic acid, which corresponds to 3D-EEM and Pearson's correlation coefficient analysis. The humification index (HIX) of HDOM increased with the rise in hydrothermal temperature (150–240 °C), as observed by the three-dimensional excitation-emission matrix spectroscopy (3D-EEMs). After reaching its peak at 240 °C, the HIX value gradually dropped in line with the trend of the DOC change. Moreover, the bioavailability (BIX) value of DOM was all high and greater than 1, indicating all the HDOM are readily bioavailable. Two microbial humic substances (C1 and C4), a humic-like substance (C2), and a protein-like substance (C3) were discovered in DOM by integrating 3D-EEMs with parallel factor analysis (PARAFAC). Their fluorescence intensity decreases as the Cu(II) concentration increases, indicating the formation of complexes with Cu(II). As the temperature rises, the binding ability of DOM and Cu(II) changes significantly, reaching the optimum at 300 °C. Meanwhile, the substance C2 has the strongest binding ability with Cu(II). This research emphasizes the significance of spectroscopy analysis in determining the evolution of hydrochar-derived DOM, the potential for heavy metal binding and migration, and its characteristics and features.
Graphical Abstract
![](http://media.springernature.com/lw685/springer-static/image/art%3A10.1007%2Fs42773-024-00353-y/MediaObjects/42773_2024_353_Figa_HTML.png)
Highlights
-
1.
The effect of temperature on the spectral properties of hydrochar-derived DOM was studied.
-
2.
The aromaticity and humification degree of HDOM were enhanced by the increase in hydrothermal temperature, which enhanced the stability of hydrochar.
-
3.
Fulvic acid and protein-like material were the dominant component, and the humic-like component (C2) had the highest binding capacity with Cu(II).
Similar content being viewed by others
Avoid common mistakes on your manuscript.
1 Introduction
Hydrothermal carbonization (HTC), a thermochemical technology, has gained recognition in recent years as an environmentally friendly and efficient approach for valorizing agroforestry residues (Cavali et al. 2023; Li et al. 2020b; Wu et al. 2021). The preparation of hydrochar is not only simple, but also has the advantages of low exhaust gas emissions and fewer mass transfer constraints (Guo et al. 2016). Hydrochar has been widely used in catalysis (Liu et al. 2016; Zeng et al. 2023), sewage treatment (Hu et al. 2021), soil remediation and improvement (Li et al. 2022b), and other fields (Cavali et al. 2023) because of its special physical–chemical characteristics, such as rich surface functional groups, multi-level pore structure (Cheng et al. 2021; Li et al. 2021; Liu et al. 2023), and a substantial amount of nutritional elements (Song et al. 2018). More importantly, returning the hydrochar to the soil was beneficial for greenhouse gas emissions mitigation and carbon sink (Malghani et al. 2014; Zhu et al. 2019), which is crucial for combating climate change and accomplishing carbon peaking and carbon neutrality targets (Lv et al. 2022; Tipping et al. 2011). When hydrochar enters environmental media (soil and water), its active component of dissolved organic matter (DOM) is released with the flow of water (Cheng et al. 2021; Zhu et al. 2019). DOM plays a crucial role in the environment, which could combine with nutrients or pollutants and undergo synergistic migration due to its water solubility and high mobility. As well as in soil and water environments, DOM can form complexes with heavy metals, including cadmium, copper, lead, etc. (Tipping et al. 2011; Ye et al. 2022). Besides, the DOM also affected the variety of the microbial population and the composition of soil aggregates (Ding et al. 2020; Guo et al. 2022a). Hence, understanding how different hydrothermal temperatures influence the properties of DOM in hydrochar is crucial. In addition, that complexation behavior can also affect the migration and toxicity of heavy metals (Aftabtalab et al. 2022). Their possible complexation behavior with pollutants also needs to be further explored.
Cu(II) is a heavy metal pollutant widely present in the environment, adversely affecting organisms and ecosystems (Rehman et al. 2019). At the same time, Cu(II) is also an effective fluorescence quencher, which can reduce or eliminate its fluorescence intensity by interacting with fluorescent groups (Liu et al. 2017). The adsorption performance and mechanism of hydrothermal carbon can be studied using this fluorescence quenching effect (Guo et al. 2022a). These studies help to understand and control the environmental impacts of Cu(II) and develop hydrothermal carbon's environmental remediation capabilities (Wang et al. 2022). However, the principles and rules of the hydrothermal carbonization temperature and the fluorescence quenching effect of copper still need to be clarified, and more experiments and theories are required to improve hydrothermal carbon's adsorption and selectivity.
Previous studies have shown that the application of sludge hydrochar increases soil DOM content (Zhu et al. 2023) and aging behavior of hydrochar in the environment leads to more DOM release and an increase in its combination with heavy metal elements within the soil (Guan et al. 2021; Xia et al. 2020). The properties of DOM from hydrochar are determined chiefly by the raw materials and the hydrothermal temperature (Sun et al. 2021). For instance, the amounts of dissolved organic carbon (DOC) and hydrophilic functional groups in peanut straw hydrochar were both higher than those in reed and spartina alterniflora hydrochar (Ji et al. 2021). In addition, as the hydrothermal temperature increased, the organic acid and phenol content in hydrochar DOM increased (Soroush et al. 2024), and the structural properties of hydrochar DOM were shown to be significantly connected to hydrothermal temperature, which influences their interaction with heavy metals (Babeker and Chen 2021). The hydrothermal temperature was confirmed to be the most critical factor affecting the properties of DOM at present.
Sawdust materials are one of the preferred raw materials for hydrothermal reactions, not only because they are renewable lignocellulosic biomass resources but also because of their excellent performance in the hydrothermal carbonization process (Cavali et al. 2023; Kabakcı and Baran 2019; Khan et al. 2021; Zhang et al. 2017). Recent studies have shown that under hydrothermal conditions, sawdust can be converted into hydrochar with a high calorific value and can be used as a soil remediation agent (Güler and Aydın Temel 2023; Khosravi et al. 2022). However, current research on the DOM characteristics of saw dust under hydrothermal conditions, especially the spectral characteristics and its ability to bind heavy metal elements, is still relatively limited.
In recent years, spectroscopic analysis technology has been broadly used to explore DOM characteristics and their interaction with pollutants due to its non-destructive, fast, and high-sensitivity nature (Ding et al. 2022; Li et al. 2018; Maqbool et al. 2020; Wang et al. 2019). For instance, the qualitative and semiquantitative analyses of DOM were carried out by using UV–Vis absorption spectroscopy and 3D-EEMs (Xi et al. 2018), and Gui et al. (2020) investigated the substance and structure of DOM in livestock and poultry manure biochar by employing UV–Vis absorption spectrum and 3D-EEMs. Moreover, the properties and mechanism of DOM’s binding to heavy metals were widely used to investigate fluorescence quenching titration and EEM-PARAFAC (Huang et al. 2019; Wang et al. 2019; Wei et al. 2020; Zhu et al. 2021). For instance, Huang et al. (2019) evaluated the properties of Cu(II) binding to DOM derived from biochar using that method. Hence, it is beneficial to use spectroscopic analysis techniques to investigate the DOM characteristics of sawdust-derived hydrochar from different hydrothermal temperatures and its complexation behavior with heavy metals.
In this work, a series of hydrochar was created by hydrothermally carbonizing sawdust, which is a typical waste biomass material, at varying temperatures from 150 and 300 °C, and its DOM was extracted using ultrapure water. The particular objectives of this work were to (1) study the effect of temperature on DOM characteristics by UV–Vis absorption spectra and 3D-EEMs analysis, (2) evaluate the potential ability of DOM complexation with Cu(II), and (3) explore the mechanism of DOM complexation with Cu(II).
2 Materials and methods
2.1 Hydrochar production and DOM extraction
The sawdust was sourced at a wood processing factory in Fengyang County, Anhui Province. The sawdust hydrochar preparation method followed our past research (Li et al. 2020a; Li et al. 2022a; Wei et al. 2022). Briefly, 200 mL super-pure water and 20 g desiccated sawdust were added in a 500 mL hydrothermal reactor (YT-500, China) at a solid-to-liquid ratio of 1:10. Then, the hydrothermal reaction was performed at a set temperature (150–300 °C, intervals of 30 °C) for a duration of 2 h, and cooled down naturally to room temperature. After that, the mixture produced a solid product (hydrochar) by centrifugation, which was dried at 45 °C.
Hydrochar and super-pure water at a ratio of solids to liquids of 1:100 (g mL−1) were added to a bottle, sonicated for 30 min, avoided light and was shaken for 24 h (25 °C, 160 rpm min−1) (Gui et al. 2020; Rajapaksha et al. 2019). After centrifugation, the liquid phase was filtered through a filter head (pore size: 0.45 μm, Polyether sulfone, Jinteng, China) and was labeled as sawdust hydrochar DOM (HDOM). The filtrate (HDOM) was stored in a brown volumetric flask and kept refrigerated at 4 °C for use (Chen et al. 2020). DOM of different hydrochar was marked as hydrochar initials and hydrothermal temperature digital (H150, H180, etc.).
The pH and the DOC content of DOM were determined, respectively, using a pH meter (PHS-3C, China) and a TOC analyzer (Shimadzu TOC-LCPH, Japan).
2.2 Spectral analysis of DOM
The UV–Vis spectrophotometer (Shimadzu, UV-2600, Japan) was used to measure the absorption spectra of DOM at a 1 nm interval from 200 to 600 nm. The DOM stock solution was deliquated to roughly 10 mg L−1 to prevent the inner filter effect of fluorescence spectroscopy (Gui et al. 2020), and the measured UV–Vis spectroscopy was used to normalize the fluorescence inner filter effect caused by concentration. The fluorescence spectrophotometer (Hitachi F-4600, Japan) was used to measure the 3D-EEMs of DOM with the following instrument settings: excitation wavelength (Ex): 200–450 nm, emission wavelength (Em): 250–550 nm, interval: 5 nm, and scanning speed: 12,000 nm min−1. The EEM spectrum was normalized using the pure water Raman peak.
2.3 Fluorescence quenching of Cu(II)
The DOM solution was diluted to 6 mg L−1 before titration to decrease the inner filter effect (Tian et al. 2021). Then 0.1 mol L−1 HCl and 0.1 mol L−1 NaOH were used to bring the pH of the DOM down to 6.0 ± 0.05 in order to avoid precipitation of Cu(II) (Chen et al. 2020). The corresponding DOM diluent (20 mL) was dispensed into a 40 mL sealed vial and 20 μL of the different concentration of Cu(II) solution (0–100 mmol L−1) was added to each sealed vial to get the set concentration of Cu(II) (0, 5, 10, 20, 40, 60, 80 and 100 μmol L−1) in the mixture solution (Zhu et al. 2021). To make sure that the complexation in the solution reached equilibrium, all of the sealed vials were continuously oscillated at 25 °C for 24 h in the dark (160 rpm min−1). All the titration experiments were carried out three times, and 3D-EEM and UV–Vis spectral measurements were measured immediately after the completion of all solution oscillations.
The modified Sterne-Volmer model was used to calculate the stability and complexation parameters between DOM and Cu(II). The calculation formula is as follows (Fan et al. 2021; Hur and Lee 2011):
where F0 and F represent the maximum fluorescence intensity (Fmax) in the absence of Cu(II) and the presence of Cu(II) at a concentration of CM, respectively; KM is the conditional stability constant, which is usually analyzed using the logarithmic conditional stability constant log KM. The f represents the proportion of fluorescent groups involved in the binding. KM and f are estimated according to the drawn F0/(F0 − F) and 1/CM linear fitting.
2.4 Data analysis
The fluorescence spectrum was analyzed by using the three-dimensional fluorescence spectrum data processing software platform (EFC) developed by China University of Geosciences and Peking University (He and Hur 2015). The Pearson correlation coefficient method was used to perform the correlation analysis of the interrelated parameters. Origin Pro2022 software was used for graphing. DOM characteristic parameters selected in this paper are shown in Table S1 (in supplementary material).
3 Results and discussion
3.1 The pH and DOC of HDOM
DOM derived from hydrochar which produced under different hydrothermal temperatures was all acidic (pH < 7, Fig. 1) and consistent with previous research indicating that hydrochar exhibits weak acidity (Sun et al. 2014) but contrary to the DOM from biochar. As hydrothermal temperatures increased from 150 °C to 240 °C, the pH value of DOM reduced by 2.2 units from 6.6 to 4.4 (Fig. 1), indicating that the formation of more acidic functional groups on the surface of the sawdust hydrochar might be produced by the production of acidic substances by the decarboxylation of sawdust at high temperatures (Hu et al. 2021; Saha et al. 2019). The research results of Babeker et al. (Babeker and Chen 2021) showed that when wood-based materials are carbonized at low temperatures (< 220 °C), the first components affected are cellulose and hemicellulose, which are converted into simple acidic compounds. This, in turn, leads to a decrease in the pH value of hydrochar-derived DOM, which is consistent with the results of this article. As the temperature further increases (> 220 °C), the structure of lignin begins to be affected, and depolymerization and dehydration reactions occur in a strongly acidic environment (Yu et al. 2018). In this test, the pH value then increased from 4.6 at 270 °C to 4.9 at 300 °C (Fig. 1), probably due to the further breakdown of acidic compounds at temperatures above 240 °C, or/and the creation of alkaline compounds in biomass during the HTC process as the hydrothermal temperature increased (Song et al. 2019a; Xu et al. 2022b).
The change tendency of DOC concentration in HDOM varying in hydrothermal temperature was opposite to that of pH (Fig. 1), and there was a significant negative correlation between pH and DOC (P < 0.01, R2 = − 0.64) due to the reality that most of the organic matter in HDOM is weakly acidic. The DOC concentration steadily increased from 19.30 mg L−1 at 150 °C to 37.29 mg L−1 at 240 °C due to high temperature strengthening the decomposition of hemicellulose or other components in sawdust, which produced more organic matter, including phenol, organic acid, furan, etc. (Dong et al. 2012). Nevertheless, the DOC concentration started to decrease at hydrothermal temperatures above 240 °C; and at 300 °C, it decreased to 8.81 mg L−1, which could be attributed to the degradation of cellulose in biomass, repolymerization of small molecular organic matter into macromolecular organic matter, and furan degradation, causing the release of DOM from hydrochar to be reduced (Nitsos et al. 2013; Saha et al. 2019). The DOC content first increased and then decreased (Fig. 1). This observation was in good agreement with that the higher HTC temperature increased the DOC content of bamboo hydrochar (180–330 °C) (Hao et al. 2018), whereas it was opposite to the finding for pig manure hydrochar (170–190 °C) (Song et al. 2020). In general, higher temperatures enhanced DOM release from hydrochar, which could be attributed to a progressive increase in biomass cracking during the HTC process. As the temperature of hydrochar formation increased, more broken hydrophobic organic molecules were enriched on the hydrochar surface, resulting in increased DOM release (Hao et al. 2018).
3.2 UV–Vis spectra and analysis of UV characteristic parameters
The UV–Vis spectrum exhibited two absorption peaks. One was at about 230 nm (Fig. 2) and corresponded to the π–π* electronic transition of C=C (Hu et al. 2021). The other was near 275 nm, which was connected to the C=C electronic transition at the π–π* level and the C=O electronic transition at the n–π* level in aromatic compounds (Fan et al. 2021). Taking the absorbance at 275 nm as an example, the UV absorbing capacity of HDOM steadily increased with increasing hydrothermal temperature, reached its peak value at 240 °C, and then began to decrease. This indicates that high-temperature sawdust hydrochar contains more monocyclic aromatic compounds (Hu et al. 2021), and affects its DOM. The HDOM extracted at a high hydrothermal temperature showed a big absorbance value (Fig. 2), indicating that it had more aromatic compounds (Hao et al. 2018).
To better examine the characteristic of DOM, UV–Vis spectra parameters were used to clarify the molecular characteristic of DOM. The parameter α(355) was often adopted to estimate the fraction of chromophoric groups present in the DOM or the relative concentration of chromophoric dissolved organic matter (CDOM) (Wang et al. 2021; Zhang et al. 2022). The value of α(355) exhibited an increase with temperature, rising from 2.76 L (mg m)−1 at 150 °C to 10.59 at 240 °C first, and then began to decrease; at 300 °C, it decreased to 5.07. This trend is consistent with the trend of DOC change (Fig. 1), which may be ascribed to the breakdown and decomposition of organic materials as the temperature rises.
SUVA254 is used to evaluate the aromaticity of HDOM. The SUVA260 index, which represents the content of hydrophobic components, can be used to characterize the hydrophobicity of DOM. These two indicators and values generally exhibit a positive correlation (Dilling and Kaiser 2002; He et al. 2021). The values of SUVA254 and SUVA260 of HDOM varying in different temperatures showed a consistent trend in this study (Table S2). In addition, the two HDOM indexes increased progressively with temperature, showing that the aromaticity and hydrophobicity of HDOM increased gradually with hydrothermal temperature. The macromolecular aromatic compounds, as well as highly hydrophobic substances, are part of the HDOM based on the two indexes analysis (Guo et al. 2022b; Huang et al. 2019). All of these showed that temperature greatly influenced the characteristics of HDOM; high temperature enhanced the aromaticity and hydrophobicity of HDOM, thereby enhancing the stability of hydrochar (Cao et al. 2022).
Spectral slope (SR) is an index usually adopted to describe the makeup and construction of DOM, and the calculation formula is presented in supplementary material. The SR value of DOM has an opposite relationship to its molecular weight, which means high SR means low molecular weight (Xiao et al. 2013; Zhang et al. 2022). Table S2 presents that the SR of HDOM increased gradually and finally decreased with the temperature increase, and it had the highest molecular weight at 240 °C. This supports the following hypothesis that the change in DOC content and UV spectrum at 240 °C, mentioned above, is due to the stage-dependent changes of HTC products of sawdust at increased hydrothermal temperatures.
The DOM composition is usually identified by the UV–Vis ratio at 300 nm to 400 nm (E3/E4), E3/E4 value > 3.5, which means the primary composition of DOM is fulvic acid. Conversely, the value < 3.5, the main composition of DOM is humic acid (Artinger et al. 2000; Kirchman 2003). Table S2 shows the E3/E4 values of HDOM were all above 3.5, indicating that the primary composition of each HDOM was fulvic acid.
3.3 3D-EEM and PARAFAC analysis and fluorescence characteristics parameters
The fluorescence contour plot of the HDOM (Fig. 3) was separated into five sections based on the method of fluorescence regional integration (FRI). The FRI theory divides the fluorescence spectrum into five regions based on the different compositions of fluorescent groups at different positions. The specific partition range and corresponding substances are shown in Table S3 (Peng et al. 2020; Song et al. 2019b), respectively.
The 3D fluorescence spectra of HDOM in different hydrochar (H150, H180, H210, H240, H270 and H300 represent DOM derived from sawdust hydrochar produced at different hydrothermal temperatures, respectively; FRI partition (I: tyrosine, II: tryptophan, III: fulvic acids, IV: soluble microbial by-products, V: humic acids))
The 3D-EEMs diagram of all the HDOM at different temperatures showed four main peaks (A–D). Peak A: 200–215 nm / 300–325 nm; peak B: 200–215 nm / 360–400 nm; peak D: 250–300 nm / 325–425 nm; peak D: 300–340 nm / 370–430 nm (Ex/Em). As the temperature of hydrothermal processes increased, the intensity of peak A (belongs to Region I) gradually weakened to disappear (Fig. 3), indicating the degradation of tyrosine is correspondingly enhanced. The fluorescence intensity of Peak B (belongs to Region III) increased, indicating an increase in fulvic acid substances. It reached the greatest fluorescence intensity at 270 °C but decreased at 300 °C, signifying the decomposition of fulvic acid at higher temperatures. The intensity of peak C (belongs to Region IV) progressively dropped, indicating a decrease in soluble microbial by-products. Peak D (belongs to Region IV) appeared with increasing temperature, indicating that high temperatures promoted the formation of humic acid organic matter.
Two typical fluorescence indices, Fn(280) and Fn(355), are used to analyze the composition and transformation of DOM (Zhang et al. 2023). The Fn(280) value is the highest fluorescence intensity in the range of Em = 340–360 nm when Ex = 280 nm, representing the proportion of protein-like compounds of DOM. The Fn(355) value is the greatest fluorescence intensity in the range of Em = 440–470 nm when Ex = 355 nm, representing the relative amount of humic-like compounds in DOM, and both of the two indices are positively correlated (Jin et al. 2020). The change of Fn(280) and Fn(355) showed the same trend (Table S4): with temperature, the proportion of compounds with protein-like properties from Fn(280) and humic-like compounds from Fn(355) increased, reaching maximum concentration at 270 °C, and slightly decreased at 300 °C.
The changes in bioavailability (BIX) and humification index (HIX) of HDOM are shown in Table S4. BIX represents the fluorescence intensity ratio at Ex = 310 nm, Em = 380, and Em = 480 nm, which reflects the autochthonous characteristics of DOM. When Ex = 254 nm, the fluorescence intensity integral ratio between Em = 435–480 and Em = 300–345 nm is referred to as HIX, indicating the humification index of DOM (Peng et al. 2020). All of the HDOM had BIX values of more than 1 (1.07–1.49), which is similar to previous research and indicates significant autochthonous characteristics and high bioavailability of HDOM (He et al. 2021). This is likely because the HTC process and the microbial breakdown course are so similar (Pages-Diaz and Huilinir 2020). The humification degree from HIX of HDOM followed the order: H240 > H270 > H300 > H210 > H180 > H150. This trend was consistent with the DOC concentration change and UV spectrum analysis, implying that the humification degree of HDOM is significantly affected by hydrothermal temperature. In addition, that trend was consistent with the change of SR and E3/E4 (in supplementary material for details) ratio values. All the results are consistent with prior research (Yang et al. 2019a), indicating that the hydrothermal process favored the development of humus and increased the level of humification.
3.4 Fluorescent components detection of EEM-PARAFAC modeling
The PARAFAC model effectively detected four fluorescent components of HDOM, containing two microbial humus substances (C1 and C4, Fig. 4), a humic-like material (C2), and a protein-like material (C3). Furthermore, the OpenFluor database was used to compare these four components with published components, using Tucker’s congruence coefficient (TCC) of at least 0.95 for both excitation and emission spectra (Murphy et al. 2014).
C1 (Ex/Em = 225, 400 nm) has been reported as a microbial humus component (Derrien et al. 2020, Derrien et al. 2019). C2 (Ex/Em = 205/240/300, 450 nm) is a humic-like substance (Chen et al. 2017; Lin and Guo 2020; Yang et al. 2019b). The C3 component is relatively unique due to its two peaks in the Em band, and it is similar to the fluorescence characteristics of protein-like compounds containing tyrosine and tryptophan found in previous studies (Kim et al. 2020; Yamashita et al. 2010). C4 (Ex/Em = 200/225/320, 390 nm) may be related to humic-like compounds generated from microbes (Chen et al. 2018; Gullian-Klanian et al. 2021).
Figure 5 displays the relative content evolution of the four fluorescent components in HDOM. The microbial humus component (C1) increased from 25% for H150 to 50% for H300 with the hydrothermal temperature increased; on the contrary, the protein-like substance (C3) decreased from 61% for H150 to 18% for H270 and H300. In addition, the fraction of humic-like compounds (C2) and microbial-derived humic-like substance (C4) showed a similar change tendency, gradually increasing with the hydrothermal temperature increasing from 150 to 240 °C, and then decreasing to their minimum values at 300 °C after reaching their maximum values, which was consistent with the DOC change (Fig. 1), and there was a significant correlation with between the DOC with C2 and C4, indicating that the C2 and C4 determined the DOC content of HDOM. The protein-like substance (C3) is the dominant fluorescent component in high-temperature DOM (H150), and the microbial humus component (C1) was in the low-temperature (H300). Noticeably, the proportion of the four components in HDOM of H270 and H300 had been fully reacted and stabilized when the temperature reached 270 °C and above (Fig. 5).
3.5 Fluorescent quenching
Cu(II) can form complexes with DOM, leading to fluorescence quenching (Mounier et al. 2011). As a fluorescence quencher, copper ions can effectively reduce fluorescence intensity through their unique chemical properties and interaction with fluorescent substances (Guo et al. 2015). This property makes copper ions very important in fluorescence titration analysis, helping to detect and quantify fluorescent substances (Xu et al. 2022a; Zhao et al. 2018). The fluorescence quenching effect is enhanced as the concentration of Cu(II) increased (Fig. 6), indicating that there was a coordination interaction between Cu(II) and HDOM. This result corresponds with prior work by Ren et al. (2020). Figure 6 clearly demonstrates that in the absence of Cu(II), microbial humus substances (C1 and C4) accounted for the bulk of HDOM. However, when Cu(II) was added, both C1 and C4 components exhibited significant fluorescence quenching.
According to previous studies, quenching can be used to determine the binding constant and complexation ratio of heavy metal ions to DOM (Wu et al. 2011, 2012). To investigate differences in the binding characters with various fluorescent compositions and DOM samples, the linear modified Stern–Volmer model, in conjunction with PARAFAC analysis, was used to research the quenching degree for HDOM constituents with Cu(II). And the complexation parameters were determined based on the Fmax numbers for each component exhibiting quenching behavior (Table 1 and Fig. S1).
Table 1 displays the effective complexation constant (log KM) and the ratio of binding fluorophore (f) to Cu(II) of the complexation reaction with HDOM, while Fig. S1 illustrates the fluorescence intensity fitting diagram of the combining of Cu(II) with HDOM. The linear association among F0/(F0 − F) and 1/Cu2+ of HDOM constituents at different temperatures was strong (R2 > 0.712), indicating that the equation can be effectively used to describe the fluorescence quenching process.
The data presented in Table 1 reveal that the effective quenching constant of Cu-DOM fell between 4.398 and 5.898. Furthermore, the effective complexation constants (log KM) of the four components with Cu(II) were 4.938–5.404, 5.166–5.898, 4.830–5.292, and 4.882–5.701, respectively. This indicates that the C2 component had the strongest binding ability with Cu(II). This may be due to the stronger affinity of humicoid (C2) to Cu(II) (Xing et al. 2020). This is consistent with the enhanced humification degree of HDOM caused by the increase in hydrothermal temperature. At the same time, the strong correlation between HIX and C2 components in Pearson correlation analysis (R2 = 0.99, P < 0.01) further confirmed this. In contrast, the C1 component had the weakest binding ability. It should be noted that, as judged from the fluorescence quenching curve, the components C1 and C4 in HDOM were affected by the quenching effect of Cu(II) more than the component C2 (Fig. 6). This is likely as a result of the more aromatic and high molecular size compounds in component C1 and C4 (Huang et al. 2021). At different temperatures, the C4 component of H150 and H300 had the highest fluorescence quenching percentage, which may mean that the C4 component interacted with Cu(II) most significantly at these temperatures. At the same time, the log KM of all components of H300 was higher, which indicates that HDOM at 300 °C had the strongest copper ion complexing ability. This may be related to the molecular structure and molecular weight caused by temperature changes (Hao et al. 2018). The quenching curve of protein-like compounds in HDOM (component C3) showed a declining trend with the addition of Cu(II) (Fig. 6). These findings suggest that protein-like components played a role in the binding of Cu(II) and HDOM. Previous investigations also discovered comparable phenomena (Wu et al. 2011; Yamashita and Jaffé 2008). The complexation of HDOM and Cu(II) can reduce the bioavailability and toxicity of Cu(II) in soil, laying the foundation for the environmental remediation application of hydrochar.
3.6 Pearson’s correlation analysis
To explore the effect of hydrothermal temperature on the content and characteristics of HDOM and to reveal the correlation between hydrothermal temperature and various parameters, Pearson's correlation coefficient was used to calculate the correlation coefficients between the pH and DOC values, the UV characteristic parameters (α(355), SUVA254, SUVA260, SR, E3/E4), and the PARAFAC components (C1, C2, C3, C4) and the HDOM fluorescent indices [HIX, BIX, Fn(280), Fn(355)]. The results are displayed in Fig. 7. Their relationship with the correlation coefficients was evaluated using Pearson’s correlation coefficient (R2). As can be seen from the figure, there was a significant correlation between the parameters. pH was negatively correlated with other parameters, except for SR, which was extremely significantly positively correlated (R2 = 0.84, P < 0.01). DOC content had a very significant positive correlation with α(355), E3/E4, SR, C2, C3, and other parameters (P < 0.01), indicating that the content and characteristics of chromophoric dissolved organic matter (CDOM) affected the DOC content of sawdust hydrochar. The positive correlation between DOC and E3/E4, C2, and C3 indicates that HDOM was mainly composed of macromolecular fulvic acid, mainly derived from C2 and C3 components, which is also consistent with the change of DOC content (Fig. 1) and the change of C2 component proportion at different temperatures (Fig. 5). SUVA254 and SUVA260 reflect the aromaticity and hydrophobicity of DOM. They had an extremely significant positive correlation with HIX, BIX, Fn(280), Fn(355), C1, C2, C3, C4, and other parameters (P < 0.01), indicating that HDOM was mainly composed of humified components with high aromaticity and hydrophobicity. HIX reflects the humification degree of DOM, and it also had a very significant positive correlation with BIX, Fn(280), Fn(355), C1, C2, C3, C4 and other parameters (P < 0.01), indicating that HDOM had a high degree of humification and was mainly determined by fulvic acid and humic-like components (C2), which can be seen from the correlation between HIX and BIX (R2 = 0.64, P < 0.01) and C2 (R2 = 0.98, P < 0.01). Fn(280) reflects the content of humic-like substances in CDOM, and it significantly correlated with humic-like components (C3) (R2 = 0.79, P < 0.01). Fn(355) reflects the content of protein-like substances in CDOM, and it had a very significant correlation with protein components (C2) (R2 = 0.99, P < 0.01). C1 and C3 had a very significant positive correlation (R2 = 0.69, P < 0.01), which is consistent with their change trend in the component proportion diagram (Fig. 5).
Pearson correlation analysis between HDOM components derived from sawdust hydrochar and pH, DOC content, UV Characteristic Parameters and fluorescence characteristics parameters (positive correlations are represented by red circles, and negative correlations by blue circles; significance level: P < 0.05 is indicated with “*”, and P < 0.01 is indicated with “**”; numbers display the correlation coefficient)
4 Conclusion
As the hydrothermal temperature increased, the DOC concentration of hydrochar increased rapidly to reach the maximum value at 240 °C (H240), then gradually dropped. The high temperature increased the aromaticity, hydrophilic, and humification properties of HDOM. These characteristics enhance the stability of hydrochar. The three main fluorescent components of HDOM are proteins, humic substances, and microbial humic substances. The capacity of Cu(II) to complex with HDOM displayed significant variations at the different hydrothermal temperatures, and at 300 °C, the HDOM component had a higher complexing concentration with Cu(II). Microbial humic substances demonstrate greater complexation ability than humic substances and protein-like substances. Spectroscopic techniques offer a quick and convenient approach to assessing the environmental impact of eco-friendly materials. This study demonstrates the potential of spectroscopic techniques to assess the environmental impact of hydrochar and other biochar materials. This study will contribute to the ongoing efforts to evaluate the environmental impact of hydrochar applications.
Data availability
The datasets used or analyzed during the current study are available from the corresponding author upon reasonable request.
References
Aftabtalab A, Rinklebe J, Shaheen SM, Niazi NK, Moreno-Jimenez E, Schaller J, Knorr KH (2022) Review on the interactions of arsenic, iron (oxy)(hydr)oxides, and dissolved organic matter in soils, sediments, and groundwater in a ternary system. Chemosphere 286:131790
Artinger R, Buckau G, Geyer S, Fritz P, Wolf M, Kim J (2000) Characterization of groundwater humic substances: influence of sedimentary organic carbon. Appl Geochem 15(1):97–116
Babeker TMA, Chen Q (2021) Heavy metal removal from wastewater by adsorption with hydrochar derived from biomass: current applications and research trends. Curr Pollut Rep 7(1):54–71
Cao Q, An T, Xie J, Liu Y, Xing L, Ling X, Chen C (2022) Insight to the physiochemical properties and DOM of biochar under different pyrolysis temperature and modification conditions. J Anal Appl Pyrol 166:105590
Cavali M, Junior NL, de Sena JD, Woiciechowski AL, Soccol CR, Belli Filho P, Bayard R, Benbelkacem H, de Castilhos Junior AB (2023) A review on hydrothermal carbonization of potential biomass wastes, characterization and environmental applications of hydrochar, and biorefinery perspectives of the process. Sci Total Environ 857:159627
Chen M, Kim SH, Jung HJ, Hyun JH, Choi JH, Lee HJ, Huh IA, Hur J (2017) Dynamics of dissolved organic matter in riverine sediments affected by weir impoundments: production, benthic flux, and environmental implications. Water Res 121:150–161
Chen B, Huang W, Ma S, Feng M, Liu C, Gu X, Chen K (2018) Characterization of chromophoric dissolved organic matter in the littoral zones of Eutrophic Lakes Taihu and Hongze during the Algal Bloom Season. Water 10(7):861
Chen B, Zhao M, Liu C, Feng M, Ma S, Liu R, Chen K (2020) Comparison of copper binding properties of DOM derived from fresh and pyrolyzed biomaterials: insights from multi-spectroscopic investigation. Sci Total Environ 721:137827
Cheng H, Ji R, Yao S, Song Y, Sun Q, Bian Y, Wang Z, Zhang L, Jiang X, Han J (2021) Potential release of dissolved organic matter from agricultural residue-derived hydrochar: insight from excitation emission matrix and parallel factor analysis. Sci Total Environ 781:146712
Derrien M, Shin KH, Hur J (2019) Biodegradation-induced signatures in sediment pore water dissolved organic matter: implications from artificial sediments composed of two contrasting sources. Sci Total Environ 694:133714
Derrien M, Lee MH, Choi K, Lee KS, Hur J (2020) Tracking the evolution of particulate organic matter sources during summer storm events via end-member mixing analysis based on spectroscopic proxies. Chemosphere 252:126445
Dilling J, Kaiser K (2002) Estimation of the hydrophobic fraction of dissolved organic matter in water samples using UV photometry. Water Res 36(20):5037–5044
Ding Y, Shi Z, Ye Q, Liang Y, Liu M, Dang Z, Wang Y, Liu C (2020) Chemodiversity of soil dissolved organic matter. Environ Sci Technol 54(10):6174–6184
Ding L, Luo Y, Yu X, Ouyang Z, Liu P, Guo X (2022) Insight into interactions of polystyrene microplastics with different types and compositions of dissolved organic matter. Sci Total Environ 824:153883
Dong C-Q, Zhang Z-F, Lu Q, Yang Y-P (2012) Characteristics and mechanism study of analytical fast pyrolysis of poplar wood. Energy Convers Manage 57:49–59
Fan X, Liu C, Yu X, Wang Y, Song J, Xiao X, Meng F, Cai Y, Ji W, Xie Y, Peng P (2021) Insight into binding characteristics of copper(II) with water-soluble organic matter emitted from biomass burning at various pH values using EEM-PARAFAC and two-dimensional correlation spectroscopy analysis. Chemosphere 278:130439
Guan J, Liu Y, Jing F, Ye R, Chen J (2021) Contrasting impacts of chemical and physical ageing on hydrochar properties and sorption of norfloxacin with coexisting Cu(2). Sci Total Environ 772:145502
Gui X, Liu C, Li F, Wang J (2020) Effect of pyrolysis temperature on the composition of DOM in manure-derived biochar. Ecotoxicol Environ Saf 197:110597
Güler B, Aydın Temel F (2023) Investigation of value-added charcoal production from full-scale hydrothermal carbonization of hazelnut husk and wood waste. Biomass Conversion and Biorefinery, 1–9
Gullian-Klanian M, Gold-Bouchot G, Delgadillo-Diaz M, Aranda J, Sanchez-Solis MJ (2021) Effect of the use of Bacillus spp. on the characteristics of dissolved fluorescent organic matter and the phytochemical quality of Stevia rebaudiana grown in a recirculating aquaponic system. Environ Sci Pollut Res Int 28(27):36326–36343
Guo X-J, Zhu N-M, Chen L, Yuan D-H, He L-S (2015) Characterizing the fluorescent properties and copper complexation of dissolved organic matter in saline-alkali soils using fluorescence excitation-emission matrix and parallel factor analysis. J Soils Sediments 15:1473–1482
Guo S, Dong X, Wu T, Zhu C (2016) Influence of reaction conditions and feedstock on hydrochar properties. Energy Convers Manage 123:95–103
Guo X, Peng Y, Li N, Tian Y, Dai L, Wu Y, Huang Y (2022a) Effect of biochar-derived DOM on the interaction between Cu(II) and biochar prepared at different pyrolysis temperatures. J Hazard Mater 421:126739
Guo Y, Zhang X, Qin X, Jiang Y, Zhu F, Xue S (2022b) Organic amendments enhanced the humification degree in soil formation of bauxite residue. Plant Soil 497(1–2):61–77
Hao S, Zhu X, Liu Y, Qian F, Fang Z, Shi Q, Zhang S, Chen J, Ren ZJ (2018) Production temperature effects on the structure of hydrochar-derived dissolved organic matter and associated toxicity. Environ Sci Technol 52(13):7486–7495
He W, Hur J (2015) Conservative behavior of fluorescence EEM-PARAFAC components in resin fractionation processes and its applicability for characterizing dissolved organic matter. Water Res 83:217–226
He C, He X, Li J, Luo Y, Li J, Pei Y, Jiang J (2021) The spectral characteristics of biochar-derived dissolved organic matter at different pyrolysis temperatures. J Environ Chem Eng 9(5):106075
Hu Z, Shi X, Jiang H (2021) Correlating the chemical properties and bioavailability of dissolved organic matter released from hydrochar of walnut shells. Chemosphere 275:130003
Huang M, Li Z, Luo N, Yang R, Wen J, Huang B, Zeng G (2019) Application potential of biochar in environment: insight from degradation of biochar-derived DOM and complexation of DOM with heavy metals. Sci Total Environ 646:220–228
Huang M, Li Z, Wen J, Ding X, Zhou M, Cai C, Shen F (2021) Molecular insights into the effects of pyrolysis temperature on composition and copper binding properties of biochar-derived dissolved organic matter. J Hazard Mater 410:124537
Hur J, Lee BM (2011) Characterization of binding site heterogeneity for copper within dissolved organic matter fractions using two-dimensional correlation fluorescence spectroscopy. Chemosphere 83(11):1603–1611
Ji R, Su L, Cheng H, Wang Y, Min J, Chen M, Li H, Chen S, Wang S, Yu G, Zhang L, Han J (2021) Insights into the potential release of dissolved organic matter from different agro-forest waste-derived hydrochars: a pilot study. J Clean Prod 319:128676
Jin M-Y, Oh H-J, Shin K-H, Jang M-H, Kim H-W, Choi B, Lin Z-Y, Heo JS, Oh J-M, Chang K-H (2020) The response of dissolved organic matter during monsoon and post-monsoon periods in the regulated river for sustainable water supply. Sustainability 12(13):5310
Kabakcı SB, Baran SS (2019) Hydrothermal carbonization of various lignocellulosics: fuel characteristics of hydrochars and surface characteristics of activated hydrochars. Waste Manage 100:259–268
Khan N, Mohan S, Dinesha P (2021) Regimes of hydrochar yield from hydrothermal degradation of various lignocellulosic biomass: a review. J Clean Prod 288:125629
Khosravi A, Zheng H, Liu Q, Hashemi M, Tang Y, Xing B (2022) Production and characterization of hydrochars and their application in soil improvement and environmental remediation. Chem Eng J 430:133142
Kim J, Kim Y, Kang H-W, Kim SH, Rho T, Kang D-J (2020) Tracing water mass fractions in the deep western Indian Ocean using fluorescent dissolved organic matter. Mar Chem 218:103720
Kirchman D (2003) The contribution of monomers and other low-molecular weight compounds to the flux of dissolved organic material in aquatic ecosystems. Aquatic ecosystems, 217–241
Li G, Khan S, Ibrahim M, Sun T-R, Tang J-F, Cotner JB, Xu Y-Y (2018) Biochars induced modification of dissolved organic matter (DOM) in soil and its impact on mobility and bioaccumulation of arsenic and cadmium. J Hazard Mater 348:100–108
Li F, Zimmerman AR, Hu X, Gao B (2020a) Removal of aqueous Cr(VI) by Zn- and Al-modified hydrochar. Chemosphere 260:127610
Li F, Zimmerman AR, Hu X, Yu Z, Huang J, Gao B (2020b) One-pot synthesis and characterization of engineered hydrochar by hydrothermal carbonization of biomass with ZnCl2. Chemosphere 254:126866
Li F, Ji W, Chen Y, Gui X, Li J, Zhao J, Zhou C (2021) Effect of temperature on the properties of liquid product from hydrothermal carbonization of animal manure and function as a heavy metal leaching agent in soil. Water Air Soil Pollut 232(5):189
Li F, Jiang Z, Ji W, Chen Y, Ma J, Gui X, Zhao J, Zhou C (2022a) Effects of hydrothermal carbonization temperature on carbon retention, stability, and properties of animal manure-derived hydrochar. Int J Agric Biol Eng 15(1):124–131
Li Q, Wang B, Zhang Q, Huang J, Ding S, Xie H, Feng Y (2022b) Water quality and periphyton functional response to input of dissolved manure-derived hydrochars (DHCs). J Environ Manage 318:115541
Lin H, Guo L (2020) Variations in colloidal DOM composition with molecular weight within individual water samples as characterized by flow field-flow fractionation and EEM-PARAFAC analysis. Environ Sci Technol 54(3):1657–1667
Liu Z, Zhang F, Hoekman SK, Liu T, Gai C, Peng N (2016) Homogeneously dispersed zerovalent iron nanoparticles supported on hydrochar-derived porous carbon: simple, in situ synthesis and use for dechlorination of PCBs. ACS Sustain Chem Eng 4(6):3261–3267
Liu S, Wang Y-M, Han J (2017) Fluorescent chemosensors for copper (II) ion: Structure, mechanism and application. J Photochem Photobiol, C 32:78–103
Liu Y-L, Zhang C, Guo L, Zeng Q, Wang R, Chen H, Zhang Q, Zeng Q (2023) Synergistically adsorbing and reducing Uranium from water by a novel nano zero-valent copper/MXene 0D/2D nanocomposite. Water Res 245:120666
Lv T, Wang B, Wang R (2022) An overview of enabling catalysts for carbon dioxide conversion aiming at the two-carbon target. Aerosol Air Qual Res 22(8):220227
Malghani S, Jüschke E, Baumert J, Thuille A, Antonietti M, Trumbore S, Gleixner G (2014) Carbon sequestration potential of hydrothermal carbonization char (hydrochar) in two contrasting soils; results of a 1-year field study. Biol Fertil Soils 51(1):123–134
Maqbool T, Ly QV, Asif MB, Ng HY, Zhang Z (2020) Fate and role of fluorescence moieties in extracellular polymeric substances during biological wastewater treatment: a review. Sci Total Environ 718:137291
Mounier S, Zhao H, Garnier C, Redon R (2011) Copper complexing properties of dissolved organic matter: PARAFAC treatment of fluorescence quenching. Biogeochemistry 106:107–116
Murphy KR, Stedmon CA, Wenig P, Bro R (2014) OpenFluor–an online spectral library of auto-fluorescence by organic compounds in the environment. Anal Methods 6(3):658–661
Nitsos CK, Matis KA, Triantafyllidis KS (2013) Optimization of hydrothermal pretreatment of lignocellulosic biomass in the bioethanol production process. Chemsuschem 6(1):110–122
Pages-Diaz J, Huilinir C (2020) Valorization of the liquid fraction of co-hydrothermal carbonization of mixed biomass by anaerobic digestion: effect of the substrate to inoculum ratio and hydrochar addition. Bioresour Technol 317:123989
Peng N, Wang K, Tu N, Liu Y, Li Z (2020) Fluorescence regional integration combined with parallel factor analysis to quantify fluorescencent spectra for dissolved organic matter released from manure biochars. RSC Adv 10(52):31502–31510
Rajapaksha AU, Ok YS, El-Naggar A, Kim H, Song F, Kang S, Tsang YF (2019) Dissolved organic matter characterization of biochars produced from different feedstock materials. J Environ Manage 233:393–399
Rehman M, Liu L, Wang Q, Saleem MH, Bashir S, Ullah S, Peng D (2019) Copper environmental toxicology, recent advances, and future outlook: a review. Environ Sci Pollut Res 26:18003–18016
Ren H, Ma F, Yao X, Shao K, Yang L (2020) Multi-spectroscopic investigation on the spatial distribution and copper binding ability of sediment dissolved organic matter in Nansi Lake, China. J Hydrol 591:125289
Saha N, Saba A, Reza MT (2019) Effect of hydrothermal carbonization temperature on pH, dissociation constants, and acidic functional groups on hydrochar from cellulose and wood. J Anal Appl Pyrol 137:138–145
Song C, Shan S, Muller K, Wu S, Niazi NK, Xu S, Shen Y, Rinklebe J, Liu D, Wang H (2018) Characterization of pig manure-derived hydrochars for their potential application as fertilizer. Environ Sci Pollut Res Int 25(26):25772–25779
Song C, Zheng H, Shan S, Wu S, Wang H, Christie P (2019a) Low-temperature hydrothermal carbonization of fresh pig manure: effects of temperature on characteristics of hydrochars. J Environ Eng 145(6):04019029
Song F, Wu F, Feng W, Liu S, He J, Li T, Zhang J, Wu A, Amarasiriwardena D, Xing B, Bai Y (2019b) Depth-dependent variations of dissolved organic matter composition and humification in a plateau lake using fluorescence spectroscopy. Chemosphere 225:507–516
Song C, Shan S, Yang C, Zhang C, Zhou X, Ma Q, Yrjälä K, Zheng H, Cao Y (2020) The comparison of dissolved organic matter in hydrochars and biochars from pig manure. Sci Total Environ 720:137423
Soroush S, Ronsse F, Verberckmoes A, Verpoort F, Park J, Wu D, Heynderickx PM (2024) Production of solid hydrochar from waste seaweed by hydrothermal carbonization: effect of process variables. Biomass Conversion Biorefinery 14(1):183–197
Sun Y, Gao B, Yao Y, Fang J, Zhang M, Zhou Y, Chen H, Yang L (2014) Effects of feedstock type, production method, and pyrolysis temperature on biochar and hydrochar properties. Chem Eng J 240:574–578
Sun Y, Xiong X, He M, Xu Z, Hou D, Zhang W, Ok YS, Rinklebe J, Wang L, Tsang DCW (2021) Roles of biochar-derived dissolved organic matter in soil amendment and environmental remediation: a critical review. Chem Eng J 424:130387
Tian Y, Wu Y, Peng Y, Guo X, Li Y, Dai B, Huang T (2021) Study on the complexation of heavy metals onto biogas slurry DOM using two-dimensional correlation spectroscopy combined with the log-transformed synchronous fluorescence spectroscopy. Environ Sci Pollut Res Int 28(18):22878–22885
Tipping E, Lofts S, Sonke JE (2011) Humic Ion-Binding Model VII: a revised parameterisation of cation-binding by humic substances. Environ Chem 8(3):225
Wang Y, Liu W, Li R, Zhang Y (2019) New insight into chemical changes between dissolved organic matter and environmental nano-CuO pollutants binding experiment using multi-spectroscopic techniques. J Mol Liq 291:111278
Wang M, Liu J, Peng L, Tian S, Yang C, Xu G, Wang D, Jiang T (2021) Estimation of the biogeochemical reactivities of dissolved organic matter from modified biochars using color. Sci Total Environ 790:147974
Wang Y, van Zwieten L, Wang H, Wang L, Li R, Qu J, Zhang Y (2022) Sorption of Pb(II) onto biochar is enhanced through co-sorption of dissolved organic matter. Sci Total Environ 825:153686
Wei J, Tu C, Yuan G, Zhou Y, Wang H, Lu J (2020) Limited Cu (II) binding to biochar DOM: evidence from C K-edge NEXAFS and EEM-PARAFAC combined with two-dimensional correlation analysis. Sci Total Environ 701:134919
Wei C, Li F, Yu Z, Ji L, Jiang F, Chen C, Yang J (2022) Enhanced adsorption of methylene blue using H2O2-modified hydrochar. Water Air Soil Pollut 233(10):422
Wu J, Zhang H, He PJ, Shao LM (2011) Insight into the heavy metal binding potential of dissolved organic matter in MSW leachate using EEM quenching combined with PARAFAC analysis. Water Res 45(4):1711–1719
Wu J, Zhang H, Yao QS, Shao LM, He PJ (2012) Toward understanding the role of individual fluorescent components in DOM-metal binding. J Hazard Mater 215–216:294–301
Wu L, Wei W, Wang D, Ni BJ (2021) Improving nutrients removal and energy recovery from wastes using hydrochar. Sci Total Environ 783:146980
Xi M, Zi Y, Wang Q, Wang S, Cui G, Kong F (2018) Assessment of the content, structure, and source of soil dissolved organic matter in the coastal wetlands of Jiaozhou Bay, China. Phys Chem Earth Parts a/b/c 103:35–44
Xia Y, Luo H, Li D, Chen Z, Yang S, Liu Z, Yang T, Gai C (2020) Efficient immobilization of toxic heavy metals in multi-contaminated agricultural soils by amino-functionalized hydrochar: performance, plant responses and immobilization mechanisms. Environ Pollut 261:114217
Xiao Y-H, Sara-Aho T, Hartikainen H, Vähätalo AV (2013) Contribution of ferric iron to light absorption by chromophoric dissolved organic matter. Limnol Oceanogr 58(2):653–662
Xing J, Xu G, Li G (2020) Analysis of the complexation behaviors of Cu (II) with DOM from sludge-based biochars and agricultural soil: effect of pyrolysis temperature. Chemosphere 250:126184
Xu J, Zhou H, Zhang Y, Zhao Y, Yuan H, He X, Wu Y, Zhang S (2022a) Copper nanoclusters-based fluorescent sensor array to identify metal ions and dissolved organic matter. J Hazard Mater 428:128158
Xu Y, Wang B, Ding S, Zhao M, Ji Y, Xie W, Feng Z, Feng Y (2022b) Hydrothermal carbonization of kitchen waste: an analysis of solid and aqueous products and the application of hydrochar to paddy soil. Sci Total Environ 850:157953
Yamashita Y, Jaffé R (2008) Characterizing the interactions between trace metals and dissolved organic matter using excitation− emission matrix and parallel factor analysis. Environ Sci Technol 42(19):7374–7379
Yamashita Y, Cory RM, Nishioka J, Kuma K, Tanoue E, Jaffé R (2010) Fluorescence characteristics of dissolved organic matter in the deep waters of the Okhotsk Sea and the northwestern North Pacific Ocean. Deep Sea Res Part II 57(16):1478–1485
Yang C, Liu Y, Sun X, Miao S, Guo Y, Li T (2019a) Characterization of fluorescent dissolved organic matter from green macroalgae (Ulva prolifera)-derived biochar by excitation-emission matrix combined with parallel factor and self-organizing maps analyses. Bioresour Technol 287:121471
Yang L, Cheng Q, Zhuang WE, Wang H, Chen W (2019b) Seasonal changes in the chemical composition and reactivity of dissolved organic matter at the land-ocean interface of a subtropical river. Environ Sci Pollut Res Int 26(24):24595–24608
Ye Q, Ding Z, Li R, Shi Z (2022) Kinetics of cadmium (Cd), nickel (Ni), and lead (Pb) release from fulvic acid: Role of re-association reactions and quantitative models. Sci Total Environ 843:156996
Yu Y, Lei Z, Yang X, Yang X, Huang W, Shimizu K, Zhang Z (2018) Hydrothermal carbonization of anaerobic granular sludge: effect of process temperature on nutrients availability and energy gain from produced hydrochar. Appl Energy 229:88–95
Zeng Q, Yang L, Zhang Q, Cai T, Wang Y, Cao Y, Lv J, Xiong Z, Wu S, Oh R (2023) Shaddock peels derived multilayer biochar with embedded CoO@Co nanoparticles for peroxymonosulfate based wastewater treatment. Chemosphere 325:138398
Zhang X, Zhang L, Li A (2017) Hydrothermal co-carbonization of sewage sludge and pinewood sawdust for nutrient-rich hydrochar production: synergistic effects and products characterization. J Environ Manage 201:52–62
Zhang F, Zhang W, Wu S, Fu X, Li S, Yue S (2022) Analysis of UV–Vis spectral characteristics and content estimation of soil DOM under mulching practices. Ecol Ind 138:108869
Zhang Z, Meng J, Chen Z, Zhou S, Zhang T, Chen Z, Liu Y, Cui J (2023) Response of dissolved organic matter to thermal stratification and environmental indication: the case of Gangnan Reservoir. Sci Total Environ 868:161615
Zhao C, Wang C-C, Li J-Q, Wang P, Ou J-Q, Cui J-R (2018) Interactions between copper (II) and DOM in the urban stormwater runoff: modeling and characterizations. Environ Technol 39(1):120–129
Zhu X, Liu Y, Li L, Shi Q, Hou J, Zhang R, Zhang S, Chen J (2019) Nonthermal air plasma dehydration of hydrochar improves its carbon sequestration potential and dissolved organic matter molecular characteristics. Sci Total Environ 659:655–663
Zhu Y, Jin Y, Liu X, Miao T, Guan Q, Yang R, Qu J (2021) Insight into interactions of heavy metals with livestock manure compost-derived dissolved organic matter using EEM-PARAFAC and 2D-FTIR-COS analyses. J Hazard Mater 420:126532
Zhu Q, Liang Y, Zhang Q, Zhang Z, Wang C, Zhai S, Li Y, Sun H (2023) Biochar derived from hydrolysis of sewage sludge influences soil properties and heavy metals distributed in the soil. J Hazard Mater 442:130053
Funding
This study was supported by the Outstanding Youth Research Project in Anhui Provincial Scientific Research Plan Project (2022AH020089); Anhui Province University Top Talent Funding Project (gxbjZD2021069); Excellent Scientific Research and Innovation Team of Universities in Anhui Province (2023AH010062) and Commissioned R&D project (ZHEP2021001, BOFA202007).
Author information
Authors and Affiliations
Contributions
Licheng Ji: Conceptualization, Methodology, Data curation, Visualization,Writing-original draft. Writing—review and editing, Project administration. Zhongpu Yu: Conceptualization, Data curation, Writing-original draft, Writing—review and editing. Qi Cao: Investigation, Validation, Formal analysis, Writing—review and editing. Xiangyang Gui: Methodology, Formal analysis, Writing—review and editing. Xingjun Fan: Methodology, Validation, Supervision. Chengcheng Wei: Investigation, Resources. Fei Jiang: Data curation, Visualization. Jie Wang: Writing—review and editing, Investigation. Fanbin Meng: Resources, Validation. Feiyue Li: Conceptualization, Funding acquisition, Project administration, Supervision, Writing—review and editing. Jianfei Wang: Conceptualization, Project administration, Writing—review and editing.
Corresponding authors
Ethics declarations
Competing interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Additional information
Handling editor: Hailong Wang
Supplementary Information
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Ji, L., Yu, Z., Cao, Q. et al. Effect of hydrothermal temperature on the optical properties of hydrochar-derived dissolved organic matter and their interactions with copper (II). Biochar 6, 64 (2024). https://doi.org/10.1007/s42773-024-00353-y
Received:
Revised:
Accepted:
Published:
DOI: https://doi.org/10.1007/s42773-024-00353-y