ABSTRACT
Various thicknesses of TiO2 films were prepared by the sol-gel method and spin-coating process. These prepared TiO2 films exhibit thickness-dependent photoelectrochemical performance. The 1.09-µm-thickTiO2 film with 20 spin-coating layers (TiO2-20) exhibits the highest short circuit current of 0.21 mAcm-2 and open circuit voltage of 0.58 V among all samples and exhibits a low PEC reaction energy barrier and fast kinetic process. Photoelectrocatalytic (PEC) degradation of methyl orange (MO) by TiO2 films was carried out under UV light. The roles of bias, film thickness, pH value, and ion properties were systematically studied because they are the four most important factors dominating the PEC performance of TiO2 films. The optimized values of bias, film thickness, and pH are 1.0 V, 1.09 µm, and 12, respectively, which were obtained according to the data of the PEC degradation of MO. The effect of ion properties on the PEC efficiency of TiO2-20 was also analyzed by using halide as targeted ions. The "activated" halide ions significantly promoted the PEC efficiency and the order was determined as Br > Cl > F. The PEC efficiency increased with increasing Cl content, up until the optimized value of 30 × 10-3 M. Finally, a complete degradation of MO by TiO2-20 was achieved in 1.5 h, with total optimization of the four factors: 1.0 V bias, 1.09-µm-thick, pH 12, and 30 × 10-3 M Cl ion content. The roles of reactive oxygen species and electric charge of photoelectrodes were also explored based on photoelectrochemical characterizations and membrane-separated reactors. Hydrogen peroxide, superoxide radical, and hydroxyl radical were found responsible for the decolorization of MO.
ABSTRACT
To enhance the electrochemical performance of MnO2/graphene composite, herein, thermally-exfoliated graphite (TE-G) is adopted as a raw material, and a hydrothermal reaction is conducted to achieve the exfoliation of TE-G and the loading of MnO2 nanosheets. Through optimizing the TE-G/KMnO4 ratio in the redox reaction between carbon and KMnO4, flower-like MnO2/G microspheres (MnO2/G-10) are obtained with 83.2% MnO2 and 16.8% residual graphene. Meanwhile, corresponding MnO2/rGO composites are prepared by using rGO as raw materials. Serving as a working electrode in a three-electrode system, MnO2/G-10 composite displays a specific capacitance of 500 F g-1 at 1 A g-1, outstanding rate performance, and capacitance retention of 85.3% for 5,000 cycles. The performance is much better than that of optimized MnO2/rGO composite. We ascribe this to the high carbon fraction in TE-G resulting in a high fraction of MnO2 in composite, and the oxygen-containing groups in rGO reduce the resulting MnO2 fraction in the composite. The superior electrochemical performance of MnO2/G-10 is dependent on the hierarchical porous structure constructed by MnO2 nanosheet arrays and the residual graphene layer in the composite. In addition, a supercapacitor assembled by TE-G negative electrode and MnO2/G positive electrode also exhibits superior performance. In consideration of the low cost of raw materials, the MnO2/G composite exhibits great application potential in the field of supercapacitors.
ABSTRACT
Molecularly imprinted polymers of glycyrrhizic acid were prepared by solution polymerization using glycyrrhizic acid as the template molecule, N-vinypyrrolidone as functional monomer, N,N-methylene bisacrylamide as cross-linker and ascorbic acid and hydrogen peroxide as initiators. Focused on the adsorption capacity and separation degree of the polymer to glycyrrhizic acid, the effects of the monomers, crosslinker and initiators were investigated and optimized. Finally, the structure of the polymer was characterized by using Fourier transform infrared spectroscopy and scanning electron microscopy. To obtain objective results, non-imprinted molecular polymers prepared under the same conditions were also characterized. The adsorption quantity of the polymer was measured by high-performance liquid chromatography. Under the optimum conditions, the maximum adsorption capacity of glycyrrhizic acid approached 15 mg/g, and the separation degree was as high as 2.5. The adsorption kinetics could be well described by a pseudo-first-order model, while the thermodynamics of the adsorption process could be described by the Langmuir model.