Advanced reduction process (ARP) has drawn an increasing interest as a new manner for removing oxidative pollutants in water. In this paper, we demonstrate the possibility of in-situ reduction of Cr(VI) by CO 2 ·- produced from formate originally existing in leather wastewater by visible-light-driven ARP containing black TiO 2 photocatalyst. The prepared black TiO 2 with nanotube structure achieves remarkable enhanced the reduction rate of Cr(VI) as high as 96.2% (k = 0.0114 min −1 ) in the presence of formate, which is approximately 4.75 times than that of 56.3% (k = 0.0024 min −1 ) in the absence under 120 min visible-light irradiate at unadjusted pH. The results exhibit a distinct contrast with commercial TiO 2 (P25). A series of control experiments are also performed, indicating that formate is able to convert the oxidative environment into a highly reductive one, and the formate concentration, black TiO 2 dosage and pH may greatly impact on the Cr(VI) reduction rate. According to the electron spin resonance (ESR) measurement, CO 2 ·- radicals can be directly verified as dominate radical in this system. Moreover, this system appears to be attractive for creating photochemical systems where in-situ production of CO 2 ·- radicals may be realized by using formate. Then this in-situ ARP system will provide a new perspective for the Cr(VI) removing, which makes leather wastewater treatment much easier and more sustainable in the future.
Rong Wang,Yue Peng,Jane Chung,Zhen Chen,Xiyang Wang,Haibo Yin,Yimin A. Wu,Jingshan Luo,Junhua Li
Summary The electrocatalytic reduction of CO 2 is an attractive method for reducing greenhouse gases and producing chemical feedstocks. However, the activation of C=O bonds limits the reaction kinetics; therefore, understanding the mechanism of C=O bond activation can guide the design of high-performance catalysts. Here, we investigate the C=O bond activation mechanism during the electroreduction of CO 2 to CO on ZnO. Using in situ experimental techniques and quantum chemical calculations , we find that defects in ZnO promote the formation of Zn–ZnO x interfaces during CO 2 reduction, which mediates an intimate-junction exciton state by the metal semiconductor heterophase. This promotes the formation of CO 2 radicals, exposing electron donation centers for CO 2 adsorption and redox centers for cleaving stable C=O bonds. The internal electric field generated by the heterojunction enhances the initial C=O activation by facilitating the interaction between the metalized Zn d-orbital and the O π -orbital in CO 2 .
Tianyou Chen,Jin Hu,Kaizhao Wang,Kaijun Wang,Weijun Zhang,Haijiao Xie,Guoyou Gan,Jin Shi
Electron transfer to CO 2 is commonly regarded as a critical step for activating CO 2 . Herein, we describe the development of a simple and effective strategy to facilitate electron transfer to CO 2 by introducing oxygen vacancies (O V ) in electrocatalysts. We discovered that stirring oxidized eutectic gallium indium is an important pretreatment step for introducing O V . In the subsequent CO 2 reduction process, the oxidized eutectic gallium indium (O-EGaIn) was reduced to the oxide-derived EGaIn (OD-EGaIn), which achieved 4 times higher Faradic efficiency for CO production than the eutectic gallium indium (EGaIn) in a tetrabutylammonium chloride/acetonitrile (Bu 4 NCl/AN) electrolytes. The XPS results showed that the O V concentration in the OD-EGaIn is much larger than that in the O-EGaIn and EGaIn samples. Electrokinetic studies indicated that the introduction of O V facilitates electron transfer to CO 2 . Density functional theory (DFT) calculations further revealed that the electrons tend to accumulate around the O V . These localized electrons then flow to the antibonding orbitals of CO 2 molecules, resulting in activating CO 2 and forming the key CO 2 •− radical.
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