Recent advances in phenazine-linked porous catalysts toward photo/electrocatalytic applications and mechanism

In recent years,porous organic catalysts have been developed and become research hotspots in photo/electrocatalysis due to their inherent pores,high specific surface area,chemical and thermal stability,and diverse functional building blocks.Phenazine-linked organic catalysts,exhibited excellent conjugation,electrical conductivity,chemical,and thermal stability,could bring in N atoms with specific numbers and positions to regulate electron levels,anchor metals,and absorb near-infrared light,which expands solar energy utilization.These advantages of the phenazine-linked catalysts attracted our group and numerous researchers to conduct experimental and computational work on photo/electrocatalytic applications and mechanisms.This review summarizes the recent significant research progress,synthesis methods,photo/electrocatalytic performance,and applications of relative phenazine-linked catalysts.Furthermore,the photo/electrocatalytic mechanism was systematized and summarized by combining experiments and density functional theory calculations simultaneously.

Hydrogen Production From Crude Bio-oil and Biomass Char by Electrochemical Catalytic Reforming

We reports an efficient approach for production of hydrogen from crude bio-oil and biomass char in the dual fixed-bed system by using the electrochemical catalytic reforming method. The maximal absolute hydrogen yield reached 110.9 g H2/kg dry biomass. The product gas was a mixed gas containing 72%H2, 26%CO2, 1.9%CO, and a trace amount of CH4. It was observed that adding biomass char （a by-product of pyrolysis of biomass） could remarkably increase the absolute H2 yield （about 20%-50%）. The higher reforming temperature could enhance the steam reforming reaction of organic compounds in crude bio-oil and the reaction of CO and H20. In addition, the CuZn-Al2O3 catalyst in the water-gas shift bed could also increase the absolute H2 yield via shifting CO to CO2.

Pd micro-nanoparticles electrodeposited on graphene/polyimide membrane for electrocatalytic oxidation of formic acid

A novel Pd electrocatalyst with flowerlike micro-nanostructures was synthesized by electrochemical deposition on a flexible graphene/polyimide（Gr/PI） composite membrane and characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD）.The Pd micro-nanoparticles were prepared on a COOH-CNTs/PI membrane as a comparative sample.The XRD and SEM investigations for Pd electrodeposition demonstrate that the particle size of Gr/PI composite membrane is smaller than that of COOH-CNTs/PI membrane,while the uniform and dense distribution of Pd micro-nanoparticles on the Gr/PI composite membrane is greater than that on the COOH-CNTs/PI membrane.The electrocatalytic properties of Pd/Gr/PI and Pd/COOH-CNTs/PI catalysts for the oxidation of formic acid were investigated by cyclic voltammetry（CV） and chronoamperometry（CA）.It is found that the electrocatalytic activity and stability of Pd/Gr/PI are superior to those of Pd/COOH-CNTs/PI catalyst.This is because smaller metal particles and higher dense distribution desirably provide abundant catalytic sites and mean higher catalytic activity.Therefore,the Pd/Gr/PI catalyst has better catalytic performance for formic acid oxidation than the Pd/COOH-CNTs/PI catalyst.

Removal of citrate and hypophosphite binary components using Fenton,photo-Fenton and electro-Fenton processes

Both citrate and hypophosphite in aqueous solution were degraded by advanced oxidation processes （Fe^2＋/H2O2, UV/Fe^2＋/H2O2, and electrolysis/Fe^2＋/H2O2） in this study. Comparison of these techniques in oxidation efficiency was undertaken. It was found that Fenton process could not completely degrade citrate in the presence of hypophosphite since it caused a series inhibition. Therefore, UV light （photo-Fenton） or electron current （electro-Fenton） was applied to improve the degradation efficiency of the Fenton process. Results showed that both photo-Fenton and electro-Fenton processes could overcome the inhibition of hypophosphite, especially the electro-Fenton.

Multifarious function layers photoanode based on g-C_3N_4 for photoelectrochemical water splitting

We report on a novel g-C3N4/TiO 2/Co-Pi photoanode combining a TiO2 protection layer, Co-Pi hole capture layer, and g-C3 N4 light-absorption layer layer for photoelectrochemical（PEC） water splitting to generate hydrogen for the first time. This new photoanode with three function layers exhibits enhanced PEC performance with a photocurrent density of 0.346 mA ·cm–2 at 1.1 V（vs. RHE）,which is approximately 3.6 times that of pure g-C3N4 photoanode. The enhanced PEC performance of g-C3N4/TiO 2/Co-Pi photoanode benefits from the following：（1） excellent visible light absorption of g-C3N4;（2） stable protection of TiO2 to improve the durability of g-C3N4 film; and（3） photogenerated holes capture Co-Pi to separate photogenerated electron-hole pairs efficiently. This promising multifarious function layers structure provides a new perspective for PEC water splitting to generate hydrogen.

Heterogeneous Photooxidation of Phenol by Catalytic Membranes

In this work the heterogenization in polymeric membranes of decatungstate,a photocatalyst for oxidation reactions,was reported.Solid state characterization techniques confirmed that the catalyst structure was preserved within the polymeric membranes.The catalytic membranes were successfully applied in the aerobic photo-oxidation of phenol,one of the main organic pollutants in wastewater,providing stable and recyclable photocatalytic systems.The dependence of the phenol degradation rate by the catalyst loading and transmembrane pressure was shown.By comparison with homogeneous reaction,the catalyst heterogenized in membrane appears to be more efficient concerning the rate of phenol photodegradation and mineralization.

Ru effect on the catalytic performance of Pd@Ru/C catalysts for methanol electro-oxidation

Pd@Ru bimetallic nanoparticles deposited on carbon black electro-catalysts have been fabricated by microwave-assisted polyol reduction method and investigated for methanol electro-oxidation （MEO）. The structure and electro-catalytic properties of the as-prepared catalysts were characterized by XRD, SEM, TEM and cyclic voltammetry （CV） techniques. The results showed that the introduction of Ru element （2-10 wt%） into Pd 20 wt%/C （hereafter, denoted as Pd/C） produced a series of core-shell structured binary catalysts. Pd@Ru 5 wt%/C （hereafter, denoted as Pd@Rus/C） catalyst displayed the highest catalytic activity towards MEO. And the mass activity of Pd@Ru5/C electrode catalyst at E = -0.038 V （vs. Hg/HgO） was 1.42 times higher than that of Pd/C electrode catalyst. In addition, the relationship between the catalytic stability for MEO on Pd@Ru/C catalysts and the value of dbp/dfp （the ratio of MEO peak current density in the negative scan and positive scan） were also investigated. The result demonstrated that Pd@Rus/C offering the smallest value of Jbp/Jfp displayed the best stable catalytic performance.

Electrochemical characterization of MnO_2 as electrocatalytic energy material for fuel cell electrode

Development of inexpensive non Pt based high electrocatalytic energy materials is the need of the hour for fuel cell electrode to produce clean alternative green energy from synthesized bio alcohol using biomass. MnO 2,electro synthesized at different current density is found to be well performed electrocatalytic material,comparable to Pt,with higher current density,very lowovervoltage for the electrochemical oxidation of methanol. From EIS study,the polarization resistance of the coated MnO 2is found to be much lowand electrical double layer capacitance is high,the effect increases with increase in current density of electro deposition. XRD,EDX and AAS analysis confirm the M nO 2deposition. The morphology of SEM images exhibits an enhanced 3D effective substrate area,for electro oxidation of the fuel. A fewnano structured grains of the deposited M nO 2is also observed at higher current density. The fact supports that a high energetic inexpensive electro catalytic material has been found for fuel cell electrode to synthesis renewable energy from methanol fuel.

Surface structure and catalytic activity of electrodeposited Ni-Fe-Co-Mo alloy electrode by partially leaching Mo and Fe

Ni-Fe-Mo-Co alloy electrode was prepared in a citrate solution by electrodeposition, and then Mo and Fe were partially leached out from the electrode in 30% KOH solution. The unique surface micromorphology of a hive-like structure was obtained with an average pore size of about 50 nm. The electrode has a very large real surface area and a stable structure. The effects of sodium molybdate concentration on the composition, surface morphology, and structure of electrodes were analyzed by EDS, SEM and XRD. The polarization curves of the different electrodes show that the catalytic activity of electrodes is strongly correlated with the mole fraction of alloy elements (Ni, Fe, Mo, Co), and the addition of cobalt element to Ni-Fe-Mo alloy improves the catalytic activity. The Ni35.63Fe24.67Mo23.52Co16.18 electrode has the best activity for hydrogen evolution reaction(HER), with an over-potential of 66.2 mV, in 30% KOH at 80 ℃ and 200 mA/cm2. The alloy maintains its good catalytic activity for HER during continuous or intermittent electrolysis. Its electrochemical activity and catalytic stability are much higher than the other iron-group with Mo alloy electrodes.

The graphene nanopowder for electro-catalytic oxidation of dopamine and uric acid in the presence of ascorbic acid

The graphene nanopowder for electro-catalytic oxidation of dopamine and uric acid in the presence of ascorbic acid has been investigated by cyclic voltammetry,linear polarization and chronoamperometry.The graphene nanopowder modified electrode was prepared using the drop coating method,which displayed excellent electrocatalytic activity towards the oxidation of dopamine and uric acid compared with the bare glassy carbon electrode in phosphate buffer solution at pH=7.0.Linear responses for dopamine and uric acid were obtained in the ranges of3.3μmol/L to 249.1μmol/L and 6.7μmol/L to 386.3μmol/L with detection limits of 1.5μmol/L and 2.7μmol/L(S/N=3),respectively.The response time was less than 2 s in case of dopamine and 3 s in case of uric acid,respectively.The results demonstrated that the graphene nanopowder had potential for detecting dopamine and uric acid.

Facile Preparation of PVA-AA/TiO2 Composite Gel Particles and Their Tunable Photo-catalytic Property for the Degradation of Methyl Orange

In the presence of titanium dioxide powder, cross-linking reaction between commercial polyvinyl alcohol(PVA)-based macromonomer and acrylic acid(AA) was initiated with potassium persulfate in an emulsifying system. As a result, PVA-AA/TiO2 composite gel particles were obtained. The morphology and composition of the particles were analyzed with scanning electron microscopy(SEM), energy scattering x-ray spectroscopy(EDS), Fourier infrared spectroscopy(FTIR), and thermogravimetric analysis(TGA). The analysis results confirmed that the particles were the expected ones. TiO2 was dispersed homogeneously within the spheroidal particles. Compared to the control gel, the composite gel particles not only contained Ti element but also showed higher thermal stability. In addition, the photo-catalytic behavior of the particles for the degradation of methyl orange contained in aqueous solution was examined. The particles exhibited photocatalytic characteristic for the degradation of the model dye, which could be modulated by simply varying the amount of cross-linking agent or TiO2. The photo-catalytic degradation percentage of methyl orange maintained at 91%-96% after using the particles three times, which indicated that TiO2 could played its role repeatedly via being fixated within polyvinyl alcohol-based gel.

Preparation and Characterization of TiO₂Photocatalytic Thin Film and Its Compounds by Micro-Arc Oxidation Technique

Mesoporous TiO2 ceramic films have been prepared upon the Ti alloy substrate by the micro-arc oxidation (MAO) technology. To enhance the photo-catalytic property of the films, Eu2O3 particles were added into the electrolyte solution of Na2CO3/Na2SiO3. Scanning electron microscope (SEM), energy dispersive (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) are employed to characterize the modified films. Diffuse reflectance spectra (DRS) test, photo-generated current test and photo decomposition test are applied to evaluate the photo-catalytic property of the modified films. The results show that Eu2O3 transformed into one-dimensional (1-D) nano-wires embedded within the composite film, and the film has high photo-catalytic property.

Photo-Catalytic Activity of Ca_1-xNi_xS Nanocrystals

Ca1-xNixS (0 ≤ x ≤ 0.05) nanocrystals have been synthesized by facile solid state reaction method. Synthesized nanocrystals are further etched with mild acid solutions to reduce the particle size, which augments the surface to volume ratio and confinement of carriers. Crystallographic and morphological characterizations of synthesized nanomaterials have been done by X-ray diffraction and electron microscopy, respectively. Comparison of the diffraction and electron microscopy studies reveal the formation of single crystalline nanostructures. Optical characterization of synthesized nanomaterials has been done by UV-vis. absorption spectroscopic studies. The photo-catalytic activity of synthesized nanomaterials under UV irradiation has been tested using methylene blue (MB) dye as a test contaminant in aqueous media. Photo-catalytic behaviour dependence on dopant concentration and etching has been thoroughly studied to explore the potential of synthesized nanomaterials for next era optoelectronic industrial applications as well as polluted water purification.

The progress of catalytic technologies in water purification:A review

Catalytic technologies have been paid increasing attention in refractory pollutants abatement due to its practical and potential values in water purification. As effective and efficient approaches for water purification, Fenton＇s reagent, ozonation, electrochemical and photocatalytic methods have been widely studied and applied in different aspects and have been reviewed by several articles. In recent years, some novel catalytic processes based on above processes have been developed for enhancing the efficiency of removing the organics from water. This review emphasized on the recent development of heterogeneous catalytic ozonation, electrocatalysis in respect of novel electrodes and electro-Fenton method, photoelectrocatalysis process and photoelectron-Fenton in water purification. It was also an attempt to propose general ideas about mechanism and principle enhancing the catalytic efficiency for the degradation and the mineralization of organics in water.

Degradation of Residual Formaldehyde in Fabric by Photo-catalysis

The residual formaldehyde （HCHO） in fabric was degraded using photo-catalysis assisted by the compound catalyst of nano-TiO2 and nano-ZnO. The effects of several factors on the degradation, such as the composing of catalyst, irradiation time, pH value and the H2CHO concentration of the immersed solution were investigated. Results showed that H2CHO of the immersed solution had degraded 93% after 5 h irradiation, and the degradation ratio of formaldehyde could be improved and the aging of the fabric can be avoided with the addition of ZnO nanoparticles and pH value of the immersed-fibric solution. The fabric with residual formaldehyde about 1 800 μg/g can be efficiently treated to satisfy the China National Standard （GB/2912.1-1998） with the photo-catalytic degradation.

Fabrication of self-organized TiO_2 nanotubes by anodic oxidation and their photocatalysis

Self-organized TiO2 nanotubes were prepared on titanium foils at anodizing voltage of 20V in 0.5% HF solution for 2030min in order to provide a novel high-efficiency photocatalyst. And the resulting TiO2 nanotubes, in periodic ring structures around their exteriors, are open on the top, while closed on the bottom. After annealing for 3h in ambient atmosphere, the anatase phase was found, with the increasing content, in the originally amorphous TiO2 nanotubes treated at 350, 400 and 450℃; whereas the rutile phase emerged at 500℃, and the nanotube architecture could be preserved till 550℃. Furthermore, TiO2 nanotubes, fabricated at anodizing voltage of 20V for 20min and then annealed at 400℃, possesses the best photo-catalytic activity, i.e. the decolourisation of methyl orange irradiated for 40min is 99.6%.

Platinum in-situ catalytic oleylamine combustion removal process for carbon supported platinum nanoparticles

Colloidal synthesis method such as oleylamine(OAm)-stabilized process is of great interest for obtaining uniform and highly dispersed platinum nanoparticle catalysts, yet the ligand may unavoidably inhibit their electro-catalytic performance. Thus, fully removing these ligands is critical to activate catalyst surface. Previous research of OAm removal process pointed that thermal annealing was the most effective way in comparison with other methods such as chemical washing, UV–Ozone irradiation and cyclic voltammetry sweeping, but generally resulting in undesired growth of platinum nanoparticle. Few studies concerning a more efficient ligand removal process have been published yet. In this work we proposed a platinum in-situ catalytic OAm combustion strategy to elucidate the removal mechanism of OAm ligands in thermal process and the key experimental parameters were also optimized. In addition, heat flow signal based on differential scanning calorimetry(DSC) measurement as a sensitive indicator, is suggested to reveal the ligand removal efficiency, which is much more reliable than the traditional spectroscopy.In comparison with commercial Pt/C sample, such a surface clean Pt/C electrocatalyst has shown an enhanced specific activity for oxygen reduction reaction. Our removal strategy and the evaluation method are highly instructive to efficient removal of different organic ligands.

Preparation of (Ti, Sn)O_2 Nano-Composite Photocatalyst by Supercritical Fluid Dry Combination Technology

A series of TiO2-SnO2 nano-sized composite photo-catalysts containing Sn (9.3%-30.1%) were prepared from TiCI4 and SnCl4·5H2O by using sol-gel, supercritical fluid dry and solid-phase reaction (SCFD) combination technology. Characterizations with X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier Transform Infrared Spectroscopy (FTIR) showed that, in addition to anatase type TiO2, a new active phase (Ti, Sn)O2 (with particle size of 2.0-4.3 nm) formed, and there were no SnO2 crystals observed in the range of the doping concentration studied. Photo-catalytic reaction of phenol was used as a model reaction to evaluate the catalytic activities of the obtained catalysts. Compared with pure TiO2 or Ti-Sn catalyst prepared with general sol-gel method, Ti-Sn nano-composite photo-catalyst thus obtained showed significant improvement in catalytic activity. The photo-catalytic degradation rate of phenol could reach as high as 93.5% after 7 h. The preparation conditions of the new phase (Ti, Sn)O2 were investigated and its catalytic mechanism was proposed. The photo-catalytic particles prepared using SCFD combination technology exhibited small particle size, large surface area and high activity.

Studies of Several Systems with Air Electrode Electro-Synthesizing H_2O_2 on the Spot for Degr ading Aniline in Aqueous

A gas diffusion electrode (air electrode) with a high current efficiency of electro\|synthesizing H 2 O 2 using O 2 in air was prepared. The several systems with air electrode as cathode of ele ctro\|synthesizing H 2 O 2 on the reaction spot for degrading aniline in aqueous--electro\|Fenton system, photo\|excitation electro\|H 2 O 2 system and photo\|electro\|Fenton system, were developed. Th e rates of decomposition of H 2 O 2 and mineralization of anil ine were experimentally measured respectively under different conditions, and th e results indicated there has an excellent parallel relation between decompositi on rate of H 2 O 2 and mineralization rate of aniline. Especia lly, photo\|electro\|Fenton system, where H 2 O 2 is decompose d the fastest, is the best system of oxidizing and degrading organic toxicants. Compared photo\|electro\|Fenton system with photo\|Fenton system, important role is revealed in the interface of air electrode. In this paper, the mineralizatio n mechanism of aniline in the photo\|electro\|Fenton system was also discussed.

Functionalization of carbon nanotubes/graphene by polyoxometalates and their enhanced photo-electrical catalysis

Carbon nanotubes and graphene are carbon-based materials, which possess not only unique structure but also prop- erties such as high surface area, extraordinary mechanical properties, high electronic conductivity, and chemical stability. Thus, they have been regarded as an important material, especially for exploring a variety of complex catalysts. Considerable efforts have been made to functionalize and fabricate carbon-based composites with metal nanoparticles. In this review, we summarize the recent progress of our research on the decoration of carbon nanotubes/graphene with metal nanoparticles by using polyoxometalates as key agents, and their enhanced photo-electrical catalytic activities in various catalytic reactions. The polyoxometalates play a key role in constructing the nanohybrids and contributing to their photo-electrical catalytic properties.