Journal of Nanoparticle Research

, 11:1805

Nano TiO2 film electrode for electrocatalytic reduction of furfural in ionic liquids

Authors

    • College of Chemistry and Materials ScienceAnhui Normal University
    • Anhui Key Laboratory of Functional Molecular SolidsAnhui Normal University
  • Yuanyuan Hou
    • College of Chemistry and Materials ScienceAnhui Normal University
  • Jianguo He
    • College of Chemistry and Materials ScienceAnhui Normal University
  • Mai Xu
    • College of Chemistry and Materials ScienceAnhui Normal University
  • Yuqing Wang
    • College of Chemistry and Materials ScienceAnhui Normal University
  • Shuxi Wang
    • College of Chemistry and Materials ScienceAnhui Normal University
  • Jian Wang
    • College of Chemistry and Materials ScienceAnhui Normal University
  • Longwu Zha
    • College of Chemistry and Materials ScienceAnhui Normal University
Brief Communication

DOI: 10.1007/s11051-009-9610-5

Cite this article as:
Chu, D., Hou, Y., He, J. et al. J Nanopart Res (2009) 11: 1805. doi:10.1007/s11051-009-9610-5

Abstract

Nanoporous TiO2 having enhanced surface area was synthesized by sol–gel method. An “environmental friendly” method for production of furfuryl alcohol was presented by electrocatalytic reduction of furfural to furfuryl alcohol in ionic liquid medium at the surface of nanoporous TiO2 film electrode. The heterogeneous catalytic redox behaviour of a nanoporous TiO2 film electrode surface was investigated by cyclic voltammetry (CV). It was found that the catalytic reduction of furfural by Ti(IV)/Ti(III) redox system on the nanoporous TiO2 film surface. The electrode reaction mechanism is called catalytic (EC′) mechanism, current density can reach 38 mA/cm2 and yielding an overall conversion efficiency of 61.7%.

Keywords

FurfuralFurfuryl alcoholIonic liquidsNanoporous TiO2 electrodeElectrocatalytic reductionSol–gel synthesis

Introduction

Furfuryl alcohol (2-furanmethanol) is an important fine chemical for the polymer industry. It is widely used in producing various synthetic fibres, rubbers, resins and farm chemicals (Chu et al. 2006; Chen et al. 2002). It can also be used as good solvent for furan resin, pigment and varnish and as rocket fuel. The main method of preparation of furfuryl alcohol is hydrogenation of furfural. However, most catalysts and solvents used for furfural hydrogenation have high toxicity and thus cause severe environmental pollution.

As electrochemical methods are simple and considerably avoid environmental pollution, many organic compounds are synthesized by such methods (Geng and Lu 2007). Recently, much effort has been directed towards the heterogeneous electrocatalytic reduction (Vassiliev et al. 2005; Chu et al. 2008a, b). Metal ionic redox couples such as Ti(IV)/Ti(III), Cr(VI)/Cr(III) were used as mediator or electron carrier (Devadoss et al. 2003; Ruotolo et al. 2006). Titanium dioxide (TiO2) is one of the most extensively studied transition metal oxide. TiO2 notably possesses properties such as excellent redox selectivity, non-toxicity, high thermal stability, low cost and easy preparation, has been most widely used and promising materials in electrocatalytic application (Chu et al. 2004, 2008a, b; Ronconi and Pereira 2001; Chen and Ma 2007).

One of the important ways to improve electrocatalytic efficiency is to prepare catalyst with enhanced surface area. In this study, nanoporous TiO2 having enhanced surface area was synthesized by sol–gel method. The nanoporous TiO2 film electrode was used for electrocatalytic reduction of furfural to furfuryl alcohol in ionic liquids. Furthermore, the electrode reaction mechanism was also discussed.

Experimental

Furfural,1-ethyl-3-methylimidazolium tetrafluoroborat ([EMIM]BF4) were obtained from Alfa aesar (Tian jin, China) and furfural was purified before use. All solutions were prepared from double distilled water. Electrochemical experiments were carried out on the CHI660 workstation (CHI, USA). 1H-NMR spectra were recorded on Bruker Avance DMX 300 instrument (300 MHz, BRUKER AV-300, Germany) in CDCl3 with Me4Si as an internal standard.

The nanoporous TiO2 film electrode employed in experiment was manufactured as follows (Vassiliev et al. 2005; Chu et al. 2008a, b; Ronconi and Pereira 2001): the precursors of Ti(OEt)4 and TiO2 sols were prepared as described in our previous studies (Chu et al. 1999, 2000; Zhou et al. 2000). The TiO2 sols coated on pure titanium substrate were annealed at 723 K for 30 min in a muffle furnace. Then they were cooled to room temperature, and this process was repeated a minimum of five times to obtain a good coating of nanoporous TiO2 over the titanium.

The morphology characterization of nano TiO2 was observed on a field emission scanning electron microscope (FE-SEM; JSM-6700F, JEOL). The crystallite size of nano TiO2 was studied with a X-ray diffractometer (XRD-6000, SHMADZU, Japan) by using Cu Ka radiation.

CV measurements were carried out using electrochemical workstation with a three-electrode system at room temperature. A nanoporous TiO2 film electrode (surface area of 0.01 cm2), a saturated calomel electrode (SCE) and a platinum foil served as working, reference and counter electrodes, respectively. The [EMIM]BF4 with micro-water was used as the electrolyte, CV was recorded in different sweep rates. Furfural in the concentration range of 0.25–4.00 M was used.

Preparative scale experiments were performed in a laboratory-made, divided H-type glass cell. An Aldrich Nafion 117-type ion-exchange membrane was used as the diaphragm. The [EMIM]BF4 with micro-water was used as catholyte and sodium sulphate solution was used as anolyte. An 12 cm2 area of nanoporous TiO2-coated titanium electrode was prepared by the method described above and used as cathode. A 13 cm2 area of dimensionally stable anode (DSA) electrode was used as an anode. The catholyte was stirred magnetically. Concentration of furfural was varied. After the completion of the electrolysis, it was extracted with ethyl ether and then product was isolated.

Results and discussion

Figure 1 shows X-ray diffraction (XRD) pattern of nano TiO2 powders. XRD results demonstrated that the TiO2 nanoparticles were of homogenous anatase structure with low crystallinity, and the average crystallite sizes calculated from Scherrer equation (λ = 0.154056 nm) were found to be about 12 nm.
https://static-content.springer.com/image/art%3A10.1007%2Fs11051-009-9610-5/MediaObjects/11051_2009_9610_Fig1_HTML.gif
Fig. 1

XRD pattern of nano TiO2 powders

Figure 2 gives the SEM micrograph of the nanoporous TiO2 film. It was clearly displayed a multiple porous network structure and average size of nanoparticle was about 40 nm and the pore diameter was about 80 nm. The big nanoparticles should be ascribed to the aggregation of small TiO2 nanoparticles during the formation of films and the multiple porous network structure contribute to the electrocatalytic reaction of the film electrode.
https://static-content.springer.com/image/art%3A10.1007%2Fs11051-009-9610-5/MediaObjects/11051_2009_9610_Fig2_HTML.jpg
Fig. 2

SEM photograph of nanoporous TiO2 film

Figure 3 shows the cyclic voltammograms recorded for the redox behaviours of the nanoporous TiO2 film electrode in the presence and absence of 4 mol/L furfural in [EMIM]BF4 at a sweep rate of 50 mV s −1 from −0.6 to −2.2 V. There are two pairs of redox peaks are due to TiO2/Ti(OH)3 couple (Ronconi and Pereira 2001; Beck and Gabriel 1985; Chu et al. 2002; Ravichandran et al. 1994) in Fig. 3a, the equations of the redox couple is as follows:
$$ {\text{TiO}}_{2} + {\text{H}}_{2} {\text{O}} + {\text{H}}^{ + } + {\text{e}}^{ - } = {\text{Ti}}\left( {\text{OH}} \right)_{3} + {\text{H}}_{2} {\text{O}} . $$
(1)
The redox peaks are highly reproducible indicating good stability of the Ti(IV)/Ti(III) species at the nanoporous TiO2 film electrode surface in [EMIM]BF4 media. It is seen that on addition of furfural (Fig. 3b), the anodic peak completely disappeared and the cathodic wave was observed in a peak shaped from a much higher value of current when compared with the Fig. 3a at the same sweep rate. The fact that no anodic wave was observed in the presence of furfural indicates the absence of Ti(III) species for oxidation on the reverse scan. The only possibility for the absence of Ti(III) species in the presence of furfural is the heterogenous catalytic chemical reaction as shown in Eq. 2, and a large amount of Ti(IV) species generated instantaneously (Ronconi and Pereira 2001; Chu et al. 2002; Ravichandran et al. 1994) result in the increase in the current value of cathodic wave.
https://static-content.springer.com/image/art%3A10.1007%2Fs11051-009-9610-5/MediaObjects/11051_2009_9610_Fig3_HTML.gif
Fig. 3

Cyclic voltammetric behaviour of the nanoporous TiO2 electrode in [EMIM]BF4: (a) without furfural and (b) with 4 mol L−1 furfural

 https://static-content.springer.com/image/art%3A10.1007%2Fs11051-009-9610-5/MediaObjects/11051_2009_9610_Figa_HTML.gif

Figure 4 shows the concentration of furfural was varied from 0.25 to 4 M. The results showed that the cathodic peak increased along with the increase of furfural concentration and a positive shift in the peak potential.
https://static-content.springer.com/image/art%3A10.1007%2Fs11051-009-9610-5/MediaObjects/11051_2009_9610_Fig4_HTML.gif
Fig. 4

Cyclic voltammetric behaviour of the nanoporous TiO2 electrode in different concentration furfural + [EMIM]BF4. Scan rate: 50.0 mV s−1; c/(mol L−1): (a) 0.25, (b) 0.50, (c) 1.00, (d) 2.00, (e) 4.00

Figure 5 shows the effect of sweep rate on ip in the presence of furfural. It was found that the cathodic peak increased with increase of sweep rate and anodic peak was absent. The result has revealed that the heterogeneous catalytic reduction is a fast and irreversible reaction (Chu et al. 2002).
https://static-content.springer.com/image/art%3A10.1007%2Fs11051-009-9610-5/MediaObjects/11051_2009_9610_Fig5_HTML.gif
Fig. 5

Cyclic voltammetric behaviour of the nanoporous TiO2 electrode in 1 mol L−1 furfural + [EMIM]BF4. Scan rate (mV s−1): (a) 20.0, (b) 40.0, (c) 60, (d) 80, (e) 100

All the results indicate that the nanoporous TiO2 film electrode behaves as a very good heterogeneous redox catalytic electrode and furfural undergoes fast chemical reduction.

Representative results are presented in Table 1, such as current density and concentration of the furfural. It was found that as the furfural concentration was increased, competitive hydrogen evolution occurred along with the redox and current efficiency was reduced. The current density decreased along with the increase of furfural concentration, probably due to furfural solution decreased in [EMIM]BF4. Product was isolated and checked for 1H-NMR spectra. The 1H-NMR results of furfuryl alcohol are as follows: 300 MHz; CDCl3; TMS, δ = 7.39 (d, 1H, J = 0.9 Hz, CH), 6.28–6.29 (m, 1H, CH), 6.33–6.35 (m, 1H, CH), 4.59 (s, 2H, CH2), 2.07 (s, 1H, OH).
Table 1

Experimental conditions and results for the electroreduction of furfural to furfuryl alcohol

Sl. No.

Weight of furfural (g)

Current density (mA/cm2)

Weight of furfuryl alcohol (g)

Current efficiency (%)

Furfuryl alcohol yield (%)

1

5.8

15

3.30

55.7

55.7

2

11.6

22

7.02

59.3

59.3

3

17.4

38

10.96

61.7

61.7

4

23.2

23

13.8

58.6

58.6

Conclusion

In conclusion, nanoporous TiO2 having enhanced surface area was synthesized by sol–gel method. We have demonstrated that the nano TiO2 film electrode can be used for electrocatalytic reduction of furfural to furfuryl alcohol in the [EMIM]BF4. The Ti/nanoporous TiO2 film electrode can be successfully used for the reduction of furfural to furfuryl alcohol. The nano TiO2 film electrode had heterogeneous electrocatalytic activities for furfural, the TiO2/Ti (OH)3 redox couple in complex film as the medium indirectly catalysed reduction of furfural. This article result also indicated that the synthesis of furfuryl alcohol has some unique advantages over the earlier chemical such as environmentally benign and simple. Under potentiostatic condition, the same electrode when reused for several runs, was found to have good reproducibility and no chemical or electrochemical deterioration occurred and without any loss in yield and current efficiency. The “green” media [EMIM]BF4 with micro-water was used as the electrolyte. Pollution problems are avoided. Improvement in the yield of the diethyl aminomalonate are targets for future research.

Acknowledgement

This work was supported by the National Natural Science Foundation of China (no. 20476001).

Copyright information

© Springer Science+Business Media B.V. 2009