Nano TiO2 film electrode for electrocatalytic reduction of furfural in ionic liquids
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- Chu, D., Hou, Y., He, J. et al. J Nanopart Res (2009) 11: 1805. doi:10.1007/s11051-009-9610-5
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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%.
KeywordsFurfuralFurfuryl alcoholIonic liquidsNanoporous TiO2 electrodeElectrocatalytic reductionSol–gel synthesis
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.
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
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.
Experimental conditions and results for the electroreduction of furfural to furfuryl alcohol
Weight of furfural (g)
Current density (mA/cm2)
Weight of furfuryl alcohol (g)
Current efficiency (%)
Furfuryl alcohol yield (%)
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.
This work was supported by the National Natural Science Foundation of China (no. 20476001).