Introduction

Bone China is a ceramic body that is traditionally used in the manufacture of translucent white tableware (Yahya et al. 2018; Toludare et al. 2019). Enhancement of the bone China body structure with nanomaterials is proposed to improve its properties and endow it with more functionality. The growing demand for bone China ceramic has led researchers to improve its physical, chemical, and mechanical properties for decorative and household applications as well as advanced applications (Toludare et al. 2019). The composition of bone China includes bone ash, kaolin, and feldspar at mass contents of 50%, 25%, and 25%, while bone China can be sintered at approximately 1250 °C (Nodeh 2017; Zhang et al. 2016). It is a highly crystalline material that contains approximately 70% crystalline components and 30% glass. The crystallinity of bone China is attributed to the presence of large amount of bone ash, which decomposes to CaO (lime), β-tricalcium phosphate (β-TCP), and H2O at high temperatures (up to 1100 °C) (Toludare et al. 2019; Ahsan et al. 2012). The crystalline phases of bone China are formed fundamentally by anorthite (CaAl2Si2O8), β-TCP (Ca3(PO4)2), and calcium aluminosilicate glass (Yahya et al. 2018; Toludare et al. 2019; Bragança and Bergmann 2008). Because of these features, bone China bodies possess high flexural strength, high chipping resistance, and high modulus of rupture; however, the Young's modulus is lower than that of hard porcelain owing to its high porosity (Batista et al. 2001).

Bone China contains recycled materials, such as bone ash (Bragança and Bergmann 2008; Carus and Bragança 2013). It has, therefore, become highly appealing because of the growing interest in recycling materials to maintain the environment. In recent decades, with the advantages of nanotechnology, researchers have made considerable efforts to enhance the properties of ceramics using nanomaterials. Improving the mechanical and physical characteristics of ceramics is challenging. The selection and concentration of nanoparticles (NPs) play a major role in controlling the material properties. There is an increasing interest in the characteristics of nanomaterials that may lead to the development of new ceramics with superior properties. Numerous studies have focused on the use of NPs, such as Al2O3, ZrO2, TiO2, and SiO2–NPs, in ceramic bodies to improve their characteristics (Rambaldi et al. 2010; Ambrosi et al. 2014; Eliyan et al. 2021; la Garza et al. 2020; Aguilar-Elguézabal et al. 2017; Bi et al. 2017; Aly and Abd‐Elhamid, 2018). NPs can be applied to ceramic bodies in various ways, such as airbrush coating on green or fired specimens and the addition of NPs as raw materials (Rambaldi et al. 2010; Ambrosi et al. 2014; Eliyan et al. 2021; la Garza et al. 2020; Aguilar-Elguézabal et al. 2017).

A significant number of experiments have been conducted to prepare SiO2–NPs due to their unique properties. SiO2–NPs have lower toxicity than other NPs, and this increases their applicability, especially in biochemical fields such as drug delivery (Esim et al. 2019). SiO2–NPs can be utilized to produce a strengthening filler for concrete and other construction composites (Jeelani et al. 2020). Furthermore, the nature of microporous SiO2–NPs has a remarkable effect on CO2 adsorption capacity due to their capillary pores as well as their photodegradation ability due to the available active sites found on SiO2–NPs surface that react with dye molecules through redox reactions, especially during radiation exposure (Aguilar-Elguézabal et al. 2017; Rafigh and Heydarinasab 2017; Xu et al 2021).

The effect of SiO2–NPs on porcelain, whose chemical structure is close to that of bone China ceramics, was examined. Desoky et al. added 10% SiO2–NPs during the preparation of porcelain and concluded that the application of these NPs led to a noticeable change in the density, porosity, and water absorption (WA) of the porcelain. The use of SiO2–NPs has also been found to improve dielectric insulating characteristics (Desouky et al. 2020). Anil et al. reported that porcelain samples containing 2% colloidal SiO2–NPs showed an increase in flexural strength and BD (Anil et al. 2009). However, the effect of SiO2–NPs addition on the properties of bone China has not been studied.

In this work, we aim to synthesize microporous SiO2–NPs with a suitable size and pores at the nanoscale and study their applicability at different concentrations in the production of bone China ceramics. Until now, and to the best of our knowledge, no study investigated the effect of the addition of microporous SiO2–NPs to bone china body. In this respect, the physical, chemical, and mechanical properties of bone China were investigated before and after the addition of SiO2–NPs to determine the effect of this addition on bone China characteristics.

Experimental

Materials

Sodium metasilicate (SMS), cetyltrimethylammonium bromide (CTAB), sodium chloride, silver nitrate, methylene blue dye, polyvinyl methacrylate, and 37% hydrochloric acid were purchased from Sigma-Aldrich and used without further purification.

The raw materials used in bone China preparation included sodium feldspar (albite; NaAlSi3O8; Minas Company, Cairo, Egypt), cattle bones from the local market, Cairo, Egypt, and kaolin (Al2Si2O5(OH)4) from Sedlecky Company, Bozicany, Czech Republic.

Methods

Preparation of microporous SiO2 –NPs

A modified method was used to prepare the microporous SiO2–NPs (Abou Rida and Harb 2014). The precursor (silica wet gel) was prepared using SMS at concentrations of 0.15% and 1.5%. The cationic surfactant, CTAB, with different weights (1 and 2 g) was dissolved in 200 ml SMS solution. The temperature was adjusted to 55 °C under constant stirring at 300 rpm, and the mixture was neutralized using 2.5% HCl in two steps. First, HCl was added dropwise until the semi-gelatinous point at pH 9–9.5, and the mixture was stirred without HCl addition for 10 min to prevent the formation of a strong silica gel. HCl was then added to the mixture until it reached a pH of 3–3.5. NaCl (10 mL, 10%) was added to the mixture under constant stirring for 20 min. After this final addition, the silica wet gel was incubated at 50 °C for 24 h without stirring. The prepared silica wet gel was washed well with distilled water using a centrifuge at 5000 rpm until complete remove of the chloride ions, followed by drying in a microwave oven (800 W) for 10 min. This drying process was conducted seven times at 10 min intervals between microwave exposures. The dried samples were calcined at 650 °C for 3 h at a heating rate of 10 °C min−1 and then milled to form a fine powder using a mortar.

SiO2–NPs characterization

The surface morphology of the prepared SiO2–NPs was observed using a scanning electron microscope (JEOL JSM-6510LB, Tokyo, Japan). Gold layer was used as a coating material for high-resolution imaging. Energy-dispersive X-ray spectroscopy (EDX) analysis was performed to determine the elemental composition.

The sizes of the pores inside the prepared SiO2–NPs were determined using a 200 kV transmission electron microscope (JEOL JEM-2100F, Tokyo, Japan) to confirm the formation of microporous SiO2–NPs. The SiO2–NPs powder was sonicated in distilled water, and the specimen was prepared for transmission electron microscopy (TEM) analysis using a drop of colloidal solution loaded onto a 400-mesh copper grid covered by an amorphous carbon film. The solvent was then evaporated at room temperature (Abou Elmaaty et al. 2018).

The crystallinity of the synthesized SiO2–NPs was determined using an X-ray diffractometer (Bruker D8 ADVANCE, Karlsruhe, Germany). The crystallite size was determined using Scherrer's Equation (Rauf et al. 2016) as follows:

$$B = K\lambda /L\cos \theta$$

where, B = FWHM (Full Width at Half Maximum); θ = Bragg angle; λ = wavelength radiation; L = Crystalline size and k = 0.9 (Scherrer constant).

The types of bonds present in the particles were determined using a confocal Raman microscope covering a range of 200–1000 cm−1 at a laser wavelength and power of 531.95 nm and 7.2 W (Jasco NRS-4500, Tokyo, Japan). The Raman data were acquired and processed using the Jasco spectroscopy software suite.

Preparation of bone China

The cattle bones under study were boiled in water to remove adhering flesh and cartilage bits and then dried in sunlight for several days. This step was repeated thrice to completely clean the bones. The dried bones were calcined at 900 °C and then milled using mortar to obtain the bone ash. The bone ash, sodium feldspar, and kaolin were sieved using nylon sieve (45 μm). The mixture was grounded for 20 min and then mixed in powder mixing machine (Mxbaoheng, USA) for 30 min at speed of 25 rpm/min.

A blank sample of bone China was prepared by mixing bone ash, feldspar, and kaolin in a weight mixing ratio of 50:25:25. These components were mixed with an appropriate amount of water to create a moldable mixture, which was then pressed into a rectangular acrylic mold (75  × 12 × 4 mm). The specimens were sintered inside an electric muffle furnace kiln at 1320 °C and then polished. These steps were repeated for the specimens prepared using microporous SiO2–NPs, as described in Table 1.

Table 1 Chemical composition of bone China samples
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Chemical composition analysis of the raw materials in bone China

The chemical composition of the starting raw materials used in bone China preparation was determined using X-ray fluorescence (XRF). Samples of the raw materials were ground through a 200-mesh sieve, and polyvinyl methacrylate was used as the binding agent. The samples were pressed manually for up to 5 t using a Herzog pressing machine (TP 60/2D, Hamburg, Germany).

Quantitative determination of the oxides, including SiO2, Al2O3, CaO, MgO, TiO2, Fe2O3, Na2O, K2O, P2O5, Cr2O3, MnO, SrO, and SO3, was accomplished via computerized XRF (Philips PW-1400, Amsterdam, Netherlands).

DSC and TGA analysis

The thermal behavior of the prepared bone China samples was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC analysis was performed to identify the difference in the amount of heat required to increase the temperature of the prepared SiO2–NPs and the bone China samples. TGA was conducted to identify weight loss during the sintering process. A differential scanning calorimeter (Setaram S60/58986, Lyon, France) was used for both DSC and TGA analyses. Then, 20 mg of each sample was analyzed in a N2 atmosphere. Alumina powder was used as a reference material, and the heat rate was maintained at 10 °C min−1.

Determination of AP, BD, and WA

The apparent porosity (AP), bulk density (BD), and water absorption (WA) were determined based on the Archimedes method according to ASTM C373 (2006).

The test specimens were dried in an oven at 150 °C until constant mass and then cooled in a desiccator to then obtain the dry weight (WD). The specimens were placed in a pan and boiled in distilled water for 5 h. They were submerged in water while boiling and then soaked in water completely for an additional 24 h without touching the sides of the vessel. After impregnation of the test specimens, the suspended weight (WS) of each specimen suspended in water was determined. Then, all excess water was removed lightly from the surfaces of the specimens using a moistened, lint-free linen or cotton cloth, and the saturated weight (WM) was obtained. The exterior volume (V), in cubic centimeters, was calculated using Eq. (1).

$$V = W_{{\text{M}}} {-}W_{{\text{S}}}$$
(1)

AP, WA, and BD were calculated using Eqs. (2), (3), and (4):

$${\text{AP}} = \left[ {\left( {W_{{\text{M}}} {-}W_{{\text{D}}} } \right)/V} \right] \times 100$$
(2)
$${\text{WA}} = \left[ {\left( {W_{{\text{M}}} {-}W_{{\text{D}}} } \right)/W_{{\text{D}}} } \right] \times 100$$
(3)
$${\text{BD}} = W_{{\text{D}}} /V$$
(4)

Three-point bending strength test

A three-point bending test was conducted using a Lloyd LRXPlus material testing machine based on ASTM C1341 (2018) at room temperature and preload speed of 21 mm/min to evaluate the flexural strength of the bone China ceramic samples. Three replicates were used for each sample to carry out bending test through the compression direction.

Self-cleaning test

The photodegradation ability of the prepared bone China was also evaluated. The samples were stained by immersing in a methylene blue dye (0.2 g L−1) for 5 min, and then dried and exposed to sunlight for 24 h. The change in color strength was determined as K/S value in the stained samples using a spectrophotometer (CM3600A; Konica Minolta, Japan). The Kubelka–Munk equation was used for the K/S value calculation in Eq (5) as follows:

$$K/S \, = \, \left( {1 - R} \right)^{2} /2R$$

where R represents the reflectance of the stained samples, K is the absorption coefficient, and S is the scattering coefficient.

A decrease in the K/S value at 600 nm indicates dye degradation, which is expressed as the self-cleaning capacity (SCC) according to Eq. (6) as follows:

$${\text{SCC }} = \, \left[ {\left( {\left( {K/S} \right)_{b} - \, \left( {K/S} \right)_{a} } \right) \, / \, \left( {K/S} \right)_{b} } \right] \, \times \, 100,$$

where (K/S)a and (K/S)b represent the color strengths before and after exposure to sunlight, respectively (Ibrahim et al. 2017).

Statistical analysis

The obtained data were analyzed based on randomized design using three replicates. The standard deviation (SD) was obtained using SPSS statistical program to evaluate the variability from the measurement values to the mean.

Results and discussion

SiO2–NPs characterization

SEM and EDX

The size and morphology of the prepared SiO2–NPs were characterized using scanning electron microscopy (SEM) after the calcination process. The results showed that the SMS and CTAB concentrations used in the SiO2–NPs preparation evidently affected the SiO2–NPs size, as displayed in Table 2.

Table 2 Effect of SMS and CTAB concentrations on SiO2–NPs size
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The SiO2–NPs prepared using 1.5% SMS and 1 g CTAB ranged from 34 to 385 nm in size, while the change in SMS concentration to 0.15% caused a decrease in their diameter to 15–370 nm. CTAB at different concentrations (1 and 2 g/200 ml SMS) was used as a nonionic surfactant to control the SiO2 particle size at the nanoscale. The SiO2–NPs diameter decreased noticeably with increasing CTAB concentration, as shown in Table 2 and Figs. 1 and 2. The diameter of the SiO2–NPs synthesized using 2 g CTAB/200 ml SMS (1.5%) ranged from 7 to 96 nm. The formation of SiO2–NPs was also confirmed by EDX analysis, which revealed the presence of both silicon and oxygen, as illustrated in Fig. 2. The SEM micrographs showed a clear variation between the traditional silica and the prepared SiO2–NPs. The prepared SiO2–NPs diameter ranged from 7 to 479 nm, while the size of traditional silica particles was in the range of 1883–28,872 nm, as shown in Fig. 1.

Fig. 1
figure 1

SEM images of a SiO2–NPs prepared using SMS (1.5%) and 1 g CTAB, b SiO2–NPs prepared using SMS (1.5%) and 2 g CTAB at different scales, c SiO2–NPs prepared using SMS (0.15%) and 1 g CTAB, d traditional silica used in bone China, e, f TEM images of SiO2–NPs prepared using SMS (1.5%) and 2 g CTAB at different scales

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The histogram of the SiO2–NPs revealed that the NPs prepared using 2 g CTAB/200 ml SMS (1.5%) showed the narrowest size range (7–96 nm) in comparison with the other prepared SiO2–NPs. In contrast, the SiO2–NPs synthesized using 1 g CTAB/200 ml SMS (1.5%) had the largest diameter, ranging from 34 to 385 nm, as shown in Fig. 2. In addition, the histogram showed a variation in NPs diameters between the NPs prepared using CTAB at the concentration of 1 g/200 ml, and SMS at different concentrations of 0.15% and 1.5%. The most of SiO2–NPs prepared with 0.15% SMS were around 50 nm, while the most of the NPs synthesized using 1.5% SMS and CTAB (1 g/200 ml) were around 150 nm. The histogram bins were 100 nm wide and centered at 50, 150, 250, and 350 nm, as shown in Fig. 2a. Furthermore, the histogram bins of the SiO2–NPs prepared using 2 g CTAB/200 ml SMS (1.5%) were 20 nm wide and centered at 10, 30, 50, 70, and 90 nm. SiO2–NPs with diameters of 20–40 nm were considered altogether as particles with a diameter of 30 nm, as illustrated in Fig. 2b.

Fig. 2
figure 2

a Histogram of SiO2–NPs prepared using different amounts of SMS and CTAB, b, c histogram and EDX spectrum of SiO2–NPs prepared using SMS (1.5%) and 2 g CTAB, respectively

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TEM analysis

SiO2–NPs can be classified into three types depending on the pore diameter: microporous (less than 2 nm), mesoporous (2–50 nm), and macroporous (more than 50 nm) [26]. TEM analysis was conducted to confirm the microporous nature of the prepared SiO2–NPs. The TEM micrographs showed the formation of microporous SiO2–NPs, including pores with diameters ranging from 1 to 2 nm, as shown in Fig. 1. The porous nature of the prepared SiO2–NPs increases the specific area and porosity because of the nanopores that impeded inside, enabling SiO2–NPs capillary action and higher water absorption capacity than traditional SiO2–NPs (Jafari et al. 2019; Gu et al. 2016).

Raman spectrum analysis

The Raman spectrum of the SiO2–NPs showed peaks at approximately 233 and 577 cm−1, indicating the presence of SiO2. The broad peak at 577 cm−1 refers to the formation of amorphous SiO2–NPs (Biswas et al. 2018; Shabir et al. 2011), as shown in Fig. 3. The observed peak in the region 380–445 cm−1 may be corresponding to O–Si–O signal in SiO2. Another peak appeared around 470 cm−1 may be attributed to Si–Si bond (Melinon et al. 1998).

Fig. 3
figure 3

Raman spectrum of microporous SiO2–NPs

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Chemical composition of raw materials

The chemical compositions of the raw materials (bone ash, feldspar, and kaolin) were determined using XRF and are listed in Table 3. Feldspar gave the highest SiO2 percentage (75.10%), followed by kaolin (48.16%) and bone ash (0.98%). Kaolin and bone ash had the highest concentrations of Al2O3 (37.04%) and CaO (40.46%). Moreover, bone China raw materials contained other components in small quantities, as tabulated in Table 3. The obtained results revealed that a higher loss of ignition (LOI) was observed in kaolin (12.98%), followed by bone ash and feldspar. Tironi et al. (2012) reported that the LOI of kaolin was 13.3%, which agrees with the results obtained in this study.

Table 3 Chemical composition of the raw materials used in bone China preparation
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Examination of bone China surface

SEM analysis

The surfaces of samples (B0 and B1) were examined using a scanning electron microscope as shown in Fig. 4. Sample B0 did not contain SiO2–NPs, while B1 contained SiO2–NPs, which revealed the stability of the SiO2–NPs in the bone China ceramic after thermal treatment at 1320 °C. The SiO2–NPs found on the surface of the B1 sample were distributed well and were spherical in shape.

Fig. 4
figure 4

SEM micrographs of a, b surface of bone China without SiO2–NPs (B0), c, d surface of bone China with SiO2–NPs (B1), e, f surfaces of fractured bone China without SiO2–NPs (B0), g, h surfaces of fractured bone China with SiO2–NPs (B1) at different scales

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Furthermore, the surfaces of fractured bone china samples were examined using SEM analysis to confirm the presence of SiO2–NPs inside the bone china structure and to compare the microstructure of the B0 and B1 samples. The obtained SEM micrographs showed that microporous SiO2–NPs are found on the B1 sample either on the surface or inside its body, comparing to that of B0, which was clear from the prepared SiO2–NPs.

XRD analysis

X-ray diffraction (XRD) analysis was conducted for the bone China samples sintered at 1320 °C to identify the different phases formed during the sintering process. B0 showed peaks related to β-TCP, anorthite, and quartz, as shown in Fig. 5 (Biswas et al. 2018; Kara and Stevens 2002; Bimson 1969). The XRD spectra of the SiO2–NPs showed a broad peak in the range of 19.68°–27.32°, indicating the formation of amorphous SiO2–NPs (Rafigh and Heydarinasab 2017; Ghani et al. 2017). The weak and single peak appeared around 27.88° after the broad peak may be attributed to small amounts of crystalline SiO2–NPs. Tsukimura et al. reported that the amorphous nanoparticles are slowly transformed to a crystalline phase because the crystalline phase is more stable than amorphous nanoparticles and found that crystalline SiO2 particles show a strong and sharp peak around 27° (Tsukimura et al. 2021).

Fig. 5
figure 5

XRD spectra of biscuit-fired bone China (B0), bone China with SiO2–NPs (B1), and SiO2–NPs

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The fired and sintered sample B1 showed a weak and broad peak at approximately 23.56°, confirming the presence of SiO2–NPs in B1 after thermal treatment at 1320 °C. The obtained peak is weak may be due to the low concentration (1%) of microporous SiO2–NPs. XRD spectrum of B1 showed peaks with lower intensities than B0. In addition, B1 exhibited lower crystallite size (46.83 nm) than B0 (47.43 nm), indicating the decrease in bone china crystallinity nature as a result of SiO2–NPs addition. The low decrease in crystallite size and crystallinity phases may be also due to the low concentration of SiO2–NPs present in B1 sample. (El-Didamony et al. 2020) reported similar results and found that the intensity of the quartz phase in ceramic engobes decreased due to the addition of SiO2–NPs.

Characterization of bone China under study

Bending test

The mechanical characteristics of the bone China samples with SiO2–NPs at different concentrations (1, 5, 10, and 15%) were identified via a bending test in comparison with those of bone China free of SiO2–NPs. Figure 6 shows the effect of the SiO2–Nps concentration on the flexural strength, which is defined as the maximum bending stress that can be applied to a material before it yields in a flexure test. B1 showed a remarkable improvement in flexural strength, which increased to 38.38 MPa compared with B0 (35.46 MPa). On the other hand, the addition of SiO2–NPs at concentrations of 5, 10, and 15% led to a notable decrease in the flexural strength, as shown in Fig. 6. SiO2–NPs at a concentration of 1% may recover the macropores found inside the bone China body, which enhances the flexural strength (Alrumaih 2019). SEM micrographs of the surface of the fractured B1 sample confirmed the presence of microporous SiO2–NPs in the macropores of bone china body as shown in Fig. 4. Therefore, the addition of SiO2–NPs at low concentration (1%) enhances the bone china strength. However, the increase in SiO2–NPs concentrations of 1% maximizes the porosity, which decreases the bone China flexural strength because of the porous nature of SiO2–NPs (Gu et al. 2016).

Fig. 6
figure 6

a Flexural strength, b Young's modulus of pure and nanostructured bone China ceramic samples with SiO2–NPs concentrations of 0%, 1%, 5%, 10%, and 15%

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Figure 6 also shows the effect of the SiO2–NPs on Young's modulus of the bone China ceramics. Young's modulus describes the elastic properties of a solid material undergoing compression or tension in only one direction. The Young's modulus of B1 exhibited an evident increase (to 10%) compared with that of B0. Moreover, the bone China samples containing SiO2–NPs at concentrations of 5, 10, and 15% (B5, B10, and B15, respectively) showed a noticeable decrease ranging from 11 to 60% in comparison with the bone China samples that did not have the SiO2 NPs, as shown in Fig. 6. The decrease in Young's modulus may be due to the reduction in the anorthite (CaO·Al2O3·2SiO2) content caused by the addition of SiO2–NPs. Pabst et al. reported that the elastic constant (Young's modulus) of dense, single-phase, isotropic polycrystalline plagioclase depends on the anorthite content (mol.%) and found that the elastic constant increases with the anorthite content (Pabst et al. 2015). In the current study, the addition of SiO2–NPs at a low concentration (1%) led to an increase in elasticity, which reveals that SiO2–NPs could be added at low concentrations to improve the mechanical properties of bone China in a cost-effective process. Based on bending test, the optimum concentration of SiO2–NPs in bone China preparation was 1%, so B1 specimens were selected to be subjected to the following tests.

Physical characteristics

The effect of the addition of SiO2–NPs at the optimum concentration (1%) on the physical characteristics of B0 and B1, namely, BD, AP, and WA, was investigated. The AP and WA percentages of B1 were higher than those of B0, as shown in Table 4. The addition of SiO2–NPs caused a decrease in the BD value compared to the original bone China (prepared without SiO2–NPs addition). El-Didamony et al. studied the physical effect of nano-silica on ceramic engobes and found that BD decreases with an increase in nano-silica concentration, which agrees with the results of the present work (El-Didamony et al. 2020). A slight decrease in BD may be due to the low concentration (1%) of SiO2–NPs used in B1 preparation, which did not significantly affect the BD of bone china. Furthermore, the capillary forces existing in the nanopores filled them with water (Kumar et al. 2015) and led to the increases in WA and AP due to the use of microporous SiO2–NPs, as seen in the TEM micrographs and displayed in Fig. 1.

Table 4 Physical characteristics of bone China samples
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Self-cleaning

The photodegradation ability of B0 and B1 samples was evaluated against methylene blue dye by direct exposure to ultraviolet radiation from sunlight. Photocatalytic activity is affected by the particle size, crystalline structure, porosity, and specific surface area of the material (Zuo et al. 2014). In photocatalytic activity, UV and visible rays were used to motivate redox reactions via activating the photocatalyst (Zhou et al. 2021). B1 showed an obvious decrease in the blue color and a degradation percentage value of 88.23%, indicating the applicability of the prepared bone China with SiO2–NPs as a photodegradable material. The photocatalytic activity of SiO2–NPs may be due to their porosity and particle size (Abou Elmaaty et al. 2021). The B0 sample showed a lower degradation percentage value of 79.83% than the B1 specimen, indicating that the presence of SiO2–NPs in the microstructure of bone china improved its photodegradation ability.

DSC and TGA

TGA/DSC analysis was performed on B0 and B1, as shown in Fig. 7. The bone China samples were subjected to a temperature range of 20–1550 °C at a heating rate of 10 °C min−1 to evaluate their thermal performance. The TGA/DSC curves of B0 showed four endothermic peaks at 272.5, 370.6, 575.3, and 1435 °C. The first and second peaks (272.5 °C and 370.6 °C, respectively) were due to the removal of water. The endothermic peak at 575.3 °C was a major peak related to the removal of the crystalline water of bone China porcelain minerals, which is the first step in the composition of bone China porcelain structures (Chakraborty 2014; Guo et al. 2020). The endothermic effect at 1435 °C is related to the crystallization of the cristobalite phase (Colombo et al. 2018; Ajanaku et al. 2016; Gualtieri 2007).

Fig. 7
figure 7

TGA/DSC curves of bone China samples a B0, b B1, c SiO2–NPs SiO2–NPs

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The TGA/DSC curves of B1 showed nine endothermic peaks at 66.8, 265.1, 576.4, 776.6, 942.9, 1042.3, 1260, 1369.9, and 1427.3 °C, as illustrated in Fig. 7. The first peak (66.8 °C) may correspond to moisture loss (Belhouchet et al. 2019). The second peak (265.1 °C) was due to the removal of water. The peaks at 576.4 °C and 776.6 °C were related to the removal of any chemically bonded water with bone China minerals and to the formation of meta-kaolinite from kaolinite (Chakraborty 2014; Ajanaku et al. 2016). The peaks observed at 942.9 °C and 1042.3 °C may be due to the crystallization of apatite (Riaz et al. 2014). The endothermic peak at 1260 °C signaled the transformation of the spinel phase to the mullite phase (Colombo et al. 2018; Gualtieri 2007). Finally, the endothermic peaks at 1369.9 °C and 1427.3 °C were related to the appearance of the cristobalite phase and the emergence of SiO2–NPs in the sample (Colombo et al. 2018; Ajanaku et al. 2016; Aras and Kristaly 2019; Yang et al. 2012).

Conclusion

In this study, microporous SiO2–NPs were utilized to improve the physical, chemical, and mechanical properties of bone China ceramics. They were prepared using a cost-effective method utilizing SMS as a precursor in the presence of CTAB as a surfactant. The optimum concentrations of SMS and CTAB required for SiO2–NPs preparation at the nanoscale were investigated. The SEM and TEM micrographs, XRD patterns, and Raman spectrum confirmed the formation of microporous SiO2–NPs. These SiO2–NPs were added to the raw materials of bone China at various concentrations to study their effect on bone China ceramic properties. The obtained results showed that B1 had the highest flexural strength and Young's modulus values among all the bone China samples and was selected for further tests. B1 showed a remarkable increase in AP and WA, whereas BD decreased. In addition, the photodegradation ability of B1 specimens was evaluated against methylene blue dye, which decomposed clearly on the B1 surface after exposure to sunlight. Moreover, the thermal behavior of the B0 and B1 samples was studied using TGA/DSC analyses.

The obtained results revealed that SiO2–NPs addition may enable bone China ceramics to be used in new fields, such as filters, bio-scaffolding, and drug delivery. Bone China contains recycled materials; therefore, it is an eco-friendly and sustainable material that can be used in advanced applications.