Di Gu

Modified hierarchical TiO2 NTs for enhanced gas phase photocatalytic activity

In this paper, three kinds of noble metal nanoparticles (NMNs) were successfully loaded on hierarchical TiO2 nanotube arrays (TiO2 NTs) to improve photocatalytic (PC) activity of gas phase pollutants. The hierarchical TiO2 NTs, with unique top-nanoporous and bottom-nanotubular structure, were prepared through a facile two-step anodization method, and then the noble metal nanoparticles were loaded on the TiO2 NTs by means of a photo-reduction method. The gas phase photocatalytic activity of TiO2 NTs and NMNs/TiO2 NTs were estimated by decomposition of gaseous methanol. The formation of Schottky junctions between TiO2 NTs and NMNs significantly improved the PC due to they could significantly accelerate the electron transfer and thus reduction of the recombination of photogenerated electrons and holes.

Solar-driven thermo- and electrochemical degradation of nitrobenzene in wastewater: Adaptation and adoption of solar STEP concept.

The STEP concept has successfully been demonstrated for driving chemical reaction by utilization of solar heat and electricity to minimize the fossil energy, meanwhile, maximize the rate of thermo- and electrochemical reactions in thermodynamics and kinetics. This pioneering investigation experimentally exhibit that the STEP concept is adapted and adopted efficiently for degradation of nitrobenzene. By employing the theoretical calculation and thermo-dependent cyclic voltammetry, the degradation potential of nitrobenzene was found to be decreased obviously, at the same time, with greatly lifting the current, while the temperature was increased. Compared with the conventional electrochemical methods, high efficiency and fast degradation rate were markedly displayed due to the co-action of thermo- and electrochemical effects and the switch of the indirect electrochemical oxidation to the direct one for oxidation of nitrobenzene. A clear conclusion on the mechanism of nitrobenzene degradation by the STEP can be schematically proposed and discussed by the combination of thermo- and electrochemistry based the analysis of the HPLC, UV-vis and degradation data. This theory and experiment provide a pilot for the treatment of nitrobenzene wastewater with high efficiency, clean operation and low carbon footprint, without any other input of energy and chemicals from solar energy.

UV-light aided photoelectrochemical synthesis of Au/TiO2 NTs for photoelectrocatalytic degradation of HPAM

TiO2 nanotube arrays (TiO2 NTs) loaded with Au nanoparticles were fabricated as an electrode for enhanced photoelectrocatalytic activity toward partially hydrolyzed polyacrylamide (HPAM) degradation. The honeycombed TiO2 NTs were prepared by a two-step anodization method and modified by Au nanoparticles via an UV-light aided photoelectrochemical process. The photoelectrocatalytic (PEC) activities of TiO2 NTs and Au/TiO2 NTs were characterized by decomposition of HPAM. The results showed that Au/TiO2 NTs exhibit much higher PEC activity than that of pristine TiO2 NTs. The size and amount of Au nanoparticles can be well controlled by adjusting the concentrations of metal ion precursor in the photoelectrochemical process. Structures, element components and morphologies of TiO2 NTs and Au/TiO2 NTs were measured by XRD, XPS, EDS and FESEM. Photoresponse of the as prepared samples were evaluated by UV-vis DRS. The UV-light aided photoelectrochemical synthesis of Au/TiO2 NTs contributes to the rational design of the plasmonic photocatalytic composite material based on wide band gap metal oxides for photoelectrochemical applications on degradation of polymers. As a consequence, an optimum loading amount of Au were obtained with weight percentage of 1.24 wt%.

A novel route to synthesize carbon spheres and carbon nanotubes from carbon dioxide in a molten carbonate electrolyzer

The process of molten salt CO2 capture and electrochemical conversion provides us with a new way to close the present carbon cycle and mitigate global climate change by transforming the greenhouse gas CO2 into carbonaceous fuels or chemicals. In this paper, carbon spheres and carbon nanotubes that can be used as a societal resource to serve mankind are synthesized from CO2 in diverse electrolyte composites with inexpensive metallic electrodes. Carbon products, subsequent to electrolysis, are characterized by EDS, SEM, TEM, Raman, TGA, FTIR, BET and XRD to reveal the elemental composition and morphological and structural features. The results demonstrate that Li–Ca–Na and Li–Ca–K carbonate electrolytes favor carbon sphere formation rather than carbon nanotube formation, and in particular, K2CO3 shows enhanced interference with carbon nanotube growth. In contrast, Li–Ca–Ba and Li–Ba carbonate composites present an increase in the carbon nanotube fraction. Additionally, CNTs generated from Li–K, Li–Ba and Li–Ca–Ba present a different diameter. In this way, the CO2-derived carbon products of carbon spheres and carbon nanotubes could be alternatively synthesized through the appropriate regulation of the electrolyte composition.

Resolving the Thermoinduced Electrochemistry for an In-Depth Understanding of the STEP Degradation of SDBS

The solar thermal electrochemical process (STEP) has sustainably accounted for the solar thermo- and electrochemical oxidation of sodium dodecyl benzene sulfonate (SDBS) fully driven by solar energy, gaining a high efficiency with a fast rate by the combination of thermochemistry and electrochemistry. In this article, thermoinduced electrochemistry was resolved for an in-depth understanding of the STEP degradation of SDBS. We employed thermodependent cyclic voltammetry, temperature-dependent fluorescence-electrochemical spectroscopy, and time-dependent electrochemical current spectroscopy for studying the electrochemistry, including the reaction, pathway, and mechanism. First, thermodependent cyclic voltammetric spectra indicated that the SDBS in sodium chloride solution is oxidized via an indirect process initialized by active chlorine, substantially accelerating and completing the oxidation process. Second, temperature-dependent fluorescence-electrochemical spectra displayed the pathway and kinetics by finding the initial desulfonation and the subsequent breaking of the alkyl side chain and benzene ring. Finally, time-dependent electrochemical current spectra demonstrated that the initial desulfonation is the fast step by generating the high current and the subsequent breaking is the slow one by a low current response, which is in agreement with the temperature-dependent fluorescence-electrochemical spectra. A panoramic view is proposed and schemed for fully understanding the process and mechanism of the STEP degradation of SDBS. Moreover, the efficiency and effectiveness of SDBS degradation were proven to be significantly enhanced by using the STEP in outdoor and indoor tests. It is a novel and energy-free route for wastewater treatment, accomplished by the synergistic use of solar energy without any other input of energy.

The adoption and mechanism of KIO4 for redox-equilibrated stabilization of FeO42− as an equalizer in water

The inherent thermodynamic instability of FeO42− in water restricts its applications in water treatment, battery, and organic synthesis. The objective of this paper was to research and develop an additive for stabilization and mechanism of aqueous FeO42− solution on the basis of a choice of the redox equilibration. In this study, it was found that FeO42− in water was stabilized by the right match and adoption of KIO4 called an equalizer. The redox thermodynamic analysis and dynamic experimental results show that the adoption of KIO4 equalizer greatly increased lifetime of FeO42− in water by orders of magnitude. The stabilization mechanism is attributed to occur via the effect of redox equilibrium of the FeO42− and the IO4− species, as well as the formation of an oxidizing chemical environment. This study opens up possibilities for stabilization of solid ferrate compounds, for example, for use in the water treatment and super-iron battery.

Photocatalytic Degradation of Gaseous Formaldehyde by Modified Hierarchical TiO2 Nanotubes at Room Temperature

As a major indoor air pollutant, formaldehyde released from building and furnishing materials is one of the main volatile organic compounds (VOCs). Hierarchical TiO2 nanotube arrays (TiO2 NTs) prepared via a facile two-step anodization showed excellent photocatalytic (PC) degradation of formaldehyde at room temperature. Modification with noble metal nanoparticles (NMNs) could further improve the PC activity of TiO2 NTs. The final products of formaldehyde degradation were detected to be CO2 and H2O, which indicated that the mineralization of formaldehyde was the major process in this PC reaction. The reaction rate constants (k) determined for the three catalysts were in the order kTiO2 NTs < kAu/TiO2 NTs < kPt/TiO2 NTs (Pt/TiO2 NTs had the highest PC ability). The significant enhancement of PC performance can be ascribed to the formation of a Schottky junction between the NMNs and TiO2 NTs.

Solar binary chemical depolymerization of lignin for efficient production of small molecules and hydrogen

In this paper, solar binary chemical depolymerization, that is Solar Thermal Electrochemical Process (STEP), was implemented for an effective breaking of lignin into small molecules and hydrogen. Compared with the conventional unitary chemical thermolysis, solar binary chemical depolymerization of lignin has high efficiencies of the liquefaction and gasification with the low coke, and accompanied by the abundant production of hydrogen. And the reaction temperature of the STEP process was greatly lowered by an intervention of the electrolysis. The results showed that the total conversion and liquefaction of the lignin yielded 87.22% and 57.72% under a constant current of 0.4 A at 340 °C. Further characterizations show that lignin has been successfully decomposed into small molecules with high added-value and hydrogen by a combination of the thermolysis and electrolysis. And the particle size of aggregates and the color degree in the lignin aqueous solution was obviously decreased after the STEP process.

Carbon Dioxide Electrolysis and Carbon Deposition in Alkaline-Earth-Carbonate-Included Molten Salts Electrolyzer

The electrochemical reduction of CO2 in molten carbonates provides a comprehensive solution to end the detrimental global climate change, and convert and store conventional electricity in a stable chemical mode. In this work, we provide experimental validation of carbon deposition in CaCO3-, SrCO3- and BaCO3-dissolved electrolytes. Carbon products aggregate on the cathodic surface and are then collected and characterized by electron dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analysis, and X-ray diffraction (XRD) analysis. The results demonstrate that the alkaline earth carbonate additives sustain continuous CO2 electrolysis and carbon electro-deposition. However, the micromorphology and microstructure of the carbon deposits are found to be significantly changed mainly because of the interface modification induced by the alkaline earth carbonate additives. In addition, a high yield of carbon nanotubes is observed in the cathodic carbon products by optimizing the electrolytic conditions. Compared to pure Li2CO3, alkaline earth carbonate additives provide carbon nanotubes with a thicker diameter and more prominent hollow structure.