Photocatalytic activity of Cu2O supported on multi layers graphene for CO2 reduction by water under batch and continuous flow

The photocatalytic activity of Cu₂O supported on multi-layers graphene for CO₂ reduction by water was studied under two hydrodynamic environments, in a slurry batch reactor and in a capillary reactor with the catalyst immobilized on the wall. Under both conditions, the major photoproduct was hydrogen observed in the gas phase, accompanied by lesser amounts of ethanol present in the aqueous solution. The maximum production rates were 2031 and 545 μmol g^− 1 h^− 1 for H₂ and CH₃CH₂OH, respectively, and were found under the hydrodynamic mode attained in the capillary reactor.     

Hydrogenation of carbon monoxide to methane over mesoporous nickel-M-alumina (M = Fe,Ni, Co,Ce, and La) xerogel catalysts

Mesoporous nickel(30 wt%)-M(10 wt%)-alumina xerogel (30Ni10MAX) catalysts with different second metal (M = Fe, Ni, Co, Ce, and La) were prepared by a single-step sol–gel method for use in the methane production from carbon monoxide and hydrogen. In the methanation reaction, yield for CH₄ decreased in the order of 30Ni10FeAX > 30Ni10NiAX > 30Ni10CoAX > 30Ni10CeAX > 30Ni10LaAX. Experimental results revealed that CO dissociation energy of the catalyst and H₂ adsorption ability of the catalyst played a key role in determining the catalytic performance of 30Ni10MAX catalyst in the methanation reaction. Optimal CO dissociation energy of the catalyst and large H₂ adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 30Ni10FeAX catalyst with the most optimal CO dissociation energy and the largest H₂ adsorption ability exhibited the best catalytic performance in terms of conversion of CO and yield for CH₄ in the methanation reaction. The enhanced catalytic performance of 30Ni10FeAX was also due to a formation of nickel–iron alloy and a facile reduction.     

The role of graphene and europium on TiO2 performance for photocatalytic hydrogen evolution

Highly efficient Eu-TiO₂/graphene composites were synthesized by a two-step method such as sol-gel and hydrothermal process. The synthesized photocatalysts were characterized by XRD, TEM, XPS, UV–vis diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy. The results confirmed that anatase Eu-TiO₂ nanoparticles with average 10 nm sizes were successfully deposited on two-dimensional graphene sheets. The UV–visible spectroscopy showed a red shift in the absorption edge of TiO₂ due to Eu doping and graphene incorporation. Moreover, effective charge separation in Eu-TiO₂/graphene composites was confirmed by PL emission spectroscopy compared to TiO₂/graphene, Eu-TiO₂ and pure TiO₂. The photocatalytic activity for H₂ evolution over prepared composites was studied under visible light irradiation (λ ≥ 400 nm). The results demonstrate that photocatalytic performance of the photocatalysts for hydrogen production increases with increasing doping concentration of Eu upto 2 at%. However, further increase in doping content above this optimum level has decreased the performance of photocatalyst. The enhanced photocatalytic performance for H₂ evolution is attributed to extended visible light absorption, suppressed recombination of electron-hole pairs due to synergistic effects of Eu and graphene.     

Pd-YSZ cermet membranes with self-repairing capability in extreme H2S conditions

A Pd-YSZ cermet membrane that performs coupled operations of hydrogen separation from a mixed-gas stream and simultaneous hydrogen production by non-galvanic water-splitting, and have high sulfur tolerance is fabricated. It is proved that in H₂S containing atmosphere the Pd-YSZ membrane has self-repairing capability, originating mainly from the conversion of Pd₄S back to metallic Pd and SO₂ by ambipolar-diffused oxygen obtained from water-splitting. The performance of membrane was analyzed at different temperatures in high H₂S containing (0–4000 ppm H₂S) mixed gas feed during the operation as a hydrogen separation membrane as well as during the coupled operation of hydrogen separation and hydrogen production. At 900 °C with the feed-stream having ≥2000 ppm H₂S, the hydrogen flux was severely affected due to the formation of some liquid phase of Pd₄S, resulting in the segregation of hydrogen permeating Pd-phase at the membrane surface. But at 800 °C, though the membrane was affected by the Pd₄S formation in high H₂S environment (up to 1200 ppm H₂S), its self-repairing capability and additional hydrogen production by water-splitting is capable of maintaining the hydrogen flux around ~1.24 cm³ (STP)/min.cm², a value expected by the same membrane while performing only the hydrogen separation function in H₂S-free environment.     

The photocatalysis of BiFeO3 disks under visible light irradiation

The photocatalytic process of BiFeO₃ disks under visible light irradiation can be termed as photo-Fenton-like reaction. The active hydroxyl radicals (•OH) generated during the photocatalytic process were quantified using a terephthalic acid (TA) fluorescence probing technique, which were proved to be greatly influenced by the loading of H₂O₂ and catalyst dosage. Our results showed that the photocatalytic efficiency was enhanced with the increasing •OH concentration. There is an optimal loading of H₂O₂ (80 mM) and catalyst dosage (2.0 g/L), at which the photocatalytic degradation rate of MO was enhanced to 97% under visible light irradiation for 3 h.     

Novel Ag2S/ZnS/carbon nanofiber ternary nanocomposite for highly efficient photocatalytic hydrogen production

Novel Ag₂S/ZnS/carbon nanofiber (CNF) ternary nanocomposite with high photocatalytic H₂ production performance was synthesized by combination of an in-situ solid-state process and a cation-exchange reaction, using organic–inorganic layered zinc hydroxide nanofibers as precursor. Moreover, the loading amount of Ag₂S nanocrystals can be readily regulated by changing the AgNO₃ concentration, and the optimized H₂ production rate was 224.9 μmol h^− 1, significantly higher than that of the reported ZnS-based composite photocatalysts. The synergistic effect of CNF and Ag₂S as water reduction and oxidation cocatalyst, respectively, can greatly suppress the charge recombination thus resulting in high photocatalytic H₂ production activity.     

Structural and proton conductivity study of P2O5-TiO2-SiO2 glasses

Proton conducting membranes for hydrogen fuel cell applications are being developed using sol–gel-derived P₂O₅-TiO₂-SiO₂ glasses. The present work is devoted to the structural analysis of P₂O₅-TiO₂-SiO₂ glasses containing controlled pore sizes and the surface area of the glasses reaching a maximum 410 m²/g, while the average pore diameter is about 2.4 nm. They were characterized by nitrogen adsorption–desorption measurements, thermal measurement as well as FTIR spectroscopy. The structural studies were based on the evolution of the intensities and profiles of certain characteristics bands in the FTIR spectra. In order to increase proton conductivity at low relative humidity, the result suggests that the mobility of proton in the P₂O₅-TiO₂-SiO₂ glasses increases with decreasing OH bonding strength. An H₂/O₂ fuel cell was constructed using the P₂O₅-TiO₂-SiO₂ glasses as electrolyte and Pt/C-loaded carbon paper sheets as electrodes. Results show that the performance of the cell is an output power of 88 μW/cm² at 30 °C with humidity.     

Efficient hydrogen production by photocatalytic water-splitting using Pt-doped TiO2 hollow spheres under visible light

Pt doped TiO₂ hollow spheres (Pt/HS-TiO₂) are prepared by a sol–gel method and characterized by XRD, SEM, TEM and UV-visible absorption spectra. In addition, Pt/HS-TiO₂ is employed as the catalyst for photocatalytic hydrogen production from water splitting under visible light irradiation. The results show that Pt/HS-TiO₂ with hollow sphere structure presents excellent photocatalytic hydrogen evolution performance. The hydrogen generation rate can reach more than 1023.71 μmol h⁻¹ g⁻¹ at room temperature and no obvious deactivation is observed after 30 h irradiation. Furthermore, the reactively of Pt/HS-TiO₂ could be reproduced in the repeated cycle. Therefore, Pt/HS-TiO₂ is a promising photocatalyst to efficiently generate hydrogen under visible-light irradiation at room temperature.     

Enhanced blue-light photocatalytic H2 production using CdS nanofiber

The photocatalytic activity of CdS nanosphere, nanorod or nanofiber was investigated for the hydrogen production from either methanol–water or sulfide/sulfite solution irradiated with blue light. The nanostructured CdS were obtained by the precipitation method at high ethylenediamine content solutions and at moderate temperature conditions. The synthesized CdS nanofiber using CS₂ as sulfur source presented the highest photocatalytic activity for the H₂ production (954 μmol h^− 1 g^− 1) in the reaction system with four blue LED lamps. This high photoactivity was attributed to the quantum confinement effect generated by the small particle size of the nanofibers (D = ~ 5 nm and L = 25 nm).     

CO2-tolerant Ni-La5.5WO11.25-δ dual-phase membranes with enhanced H2 permeability

Enhancing the ambi-polar conductivity of the ceramic hydrogen permeable membrane by introducing an electron conductive metallic phase is quite effective, which is helpful for the hydrogen permeation flux improvement. To develop CO₂-tolerant hydrogen permeable membranes with better hydrogen permeability, Ni-La_5.5WO_11.25-δ (Ni-LWO) cermet membranes are fabricated. The alkaline earth metal-free ceramic LWO is used as the main proton-conductive phase and Ni is used as the main electron-conductive phase. The Ni-LWO membrane exhibits good chemical stability in CO₂-containing atmosphere since its hydrogen permeability maintains well in the measurement for about 180 h. Compared with the LWO ceramic membrane, the hydrogen permeability of the Ni-LWO membrane has been improved significantly. The Ni/LWO ratio has great impact on the performance of the cermet membrane. Meanwhile, among all the dual-phase Ni-LWO membranes with different Ni/LWO volume ratios, the membrane with 60 vol% Ni shows the highest hydrogen permeation flux of 0.18 ml min⁻¹ cm⁻² at 1000 °C when the feed gas contains 50% H₂.     

Large enhancements in hydrogen production of TiO2 through a simple carbon decoration

A simple carbon decoration, involving only immersion in adipic acid followed by calcination in N₂ atmosphere, was developed to prepare thin carbon layer decorated TiO₂ nanoparticles. The thin carbon layer was in tight contact with the TiO₂ domain and served as an electron trapping center to improve charge separations necessary for enhancement in photocatalytic water splitting performance of the TiO₂ nanoparticles. With an optimal carbon loading of 0.3 wt%, a fourfold improvement was achieved for hydrogen production as compared with that achieved by pristine TiO₂ nanoparticles. This simple carbon decoration provides a promising low-cost alternative to traditional Pt-decoration approaches for enhancing hydrogen productions from photocatalytic water splitting.     

A highly efficient and noble metal-free photocatalytic system using NixB/CdS as photocatalyst for visible light H2 production from aqueous solution

Photocatalytic H₂ production from water is one of the most attractive issues for the conversion of solar energy into chemical energy. In this study, the Ni_xB/CdS photocatalyst was firstly used for photocatalytic H₂-evolution reaction and showed efficient visible-light photocatalytic activity and good stability for H₂-evolution from aqueous solution. The optimal Ni_xB loading content was determined to be 0.8 wt.%, and the corresponding H₂-production rate reached up to 4.8 mmol·h^− 1·g^− 1 after a 10 h visible light irradiation. It is proposed that the loading of Ni_xB on the surface of CdS could effectively increase the separation of photo-generated electrons and holes and greatly enhance the photocatalytic activity.     

Improvement of sensitive Ni(OH)2 nonenzymatic glucose sensor based on carbon nanotube/polyimide membrane

An improved nonenzymatic glucose sensor was fabricated of Ni(OH)₂ on carbon nanotube/polyimide (PI/CNT) membrane by a simple electrochemical method. Three different morphologies of Ni(OH)₂ have been formed by changing the conditions used in synthesis process. The formation mechanism for Ni(OH)₂ nanospheres was studied to provide a deep understanding of crystal growth. The electrochemical behaviors of different Ni(OH)₂ nanostructures were investigated by cyclic voltammetry and chronoamperometry in alkaline solution. At an applied potential of +0.60 V, the sensor based on PI/CNT–Ni(OH)₂ nanospheres shows a high sensitivity of 2071.5 μA mM⁻¹ cm⁻² and a detection limit of 0.36 μM (signal/noise = 3). The proposed sensor exhibits high sensitivity, long-term stability and good reproducibility, and performs well for detection of glucose in human blood serums. Therefore, this novel fabrication method for glucose sensor is promising for the future development of nonenzymatic glucose sensors.     

Optimization of carbamazepine removal in O3/UV/H2O2 system using a response surface methodology with central composite design

This study used an ozone/ultraviolet/hydrogen peroxide (O₃/UV/H₂O₂) system to remove carbamazepine (CBZ) from water using a second-order response surface methodology (RSM) experiment with a five-level full-factorial central composite design (CCD) for optimization. The effects of both the primary and secondary interactions of the photocatalytic reaction variables, including O₃ concentration (X₁), H₂O₂ concentration (X₂), and UV intensity (X₃), were examined. The O₃ concentration significantly influenced CBZ and total organic carbon (TOC) removal as well as total inorganic nitrogen ion production (T-N) (p < 0.001). However, CBZ, TOC removal, and T-N production were enhanced with increasing O₃ and H₂O₂ concentrations up to certain levels, and further increases in O₃ and H₂O₂ resulted in adverse effects due to hydroxyl radical scavenging by higher oxidant and catalyst concentrations. UV intensity had the most significant effect on T-N production (p < 0.001). Complete removal of CBZ was achieved after 5 min. However, only 34.04% of the TOC and 36.99% of T-N were removed under optimal concentrations, indicating formation of intermediate products during CBZ degradation. The optimal ratio of O₃ (mg L^? 1): H₂O₂ (mg L^? 1): UV (mW cm^? 2) were 0.91:5.52:2.98 for CBZ removal, 0.7:18.93:12.67 for TOC removal, and 0.94: 4.85:9.03 for T-N production, respectively.     

Catalytic hydrogen production from 2-propanol in supercritical water: Comparison of some metal catalysts

The gasification of organics in supercritical water is a promising method for the direct production of hydrogen at high pressures, and in order to improve the hydrogen yield or selectivity, activities of various catalysts are evaluated. In this study, hydrogen production from 2-propanol over Ni/Al₂O₃ and Fe–Cr catalysts was investigated in supercritical water. The experiments were carried out in the temperature range of 400–600 °C and in the reaction time range of 10–30 s, under a pressure of 25 MPa. The hydrogen yields and selectivities of Ni/Al₂O₃ and Fe–Cr used in this study, and those of Pt/Al₂O₃ and Ru/Al₂O₃ used in our previous work were compared. The hydrogen contents of the gaseous products obtained by using Ni/Al₂O₃ and Fe–Cr were measured as 62 mol% and 70 mol%, respectively, at low temperatures and reaction times. However, the hydrogen yields remained in low levels when compared with that of Pt/Al₂O₃ used in previous study. Pt/Al₂O₃ was established to be the most effective and selective catalyst for hydrogen production. During the catalytic gasification of a 0.5 M solution of 2-propanol, hydrogen content up to 96 mol% and hydrogen yield of 1.05 mol/mol 2-propanol were obtained.     

Preparation of ZnIn2S4/K2La2Ti3O10 composites and their photocatalytic H2 evolution from aqueous Na2S/Na2SO3 under visible light irradiation

ZnIn₂S₄/K₂La₂Ti₃O₁₀ composite photocatalysts were synthesized via a hydrothermal route. The photocatalysts were characterized by the X-ray diffraction, scanning electron microscopy, ultraviolet–visible (UV–vis) diffuse reflection spectra and photoluminescence measurements. The UV–vis results indicated that ZnIn₂S₄/K₂La₂Ti₃O₁₀ has a strong absorption in the visible light region. The compositions of ZnIn₂S₄/K₂La₂Ti₃O₁₀ composite photocatalysts were optimized according to the photocatalytic activity for hydrogen production from aqueous Na₂S/Na₂SO₃. The composite photocatalyst loading 25 wt.% ZnIn₂S₄ exhibited the highest photocatalytic activity, the amount of H₂ production was 6.29 mmol/g after 3 h irradiation under visible light irradiation.     

Effect of Pt loading and calcination temperature on the photocatalytic hydrogen production activity of TiO2 microspheres

TiO₂ microspheres were synthesized by hydrothermal reaction using Ti(OBu)₄ as the precursor. In order to enhance the efficiency of water splitting by the TiO₂ microspheres, Pt-modified TiO₂ microspheres were prepared by the impregnation-reduction method. The diameter of TiO₂ microspheres is around 5–10 μm. The photocatalytic performances of the catalysts were measured by hydrogen generation from a mixture of water and methanol under UV light irradiation. The photocatalytic activity of the TiO₂ microspheres was remarkably enhanced by loading Pt. The optimal Pt loading is 1.2 wt%. Pt/TiO₂ microspheres exhibit about 125 times greater H₂ production rate than the unmodified TiO₂ microspheres. The effect of calcination temperature on photocatalytic activity of the TiO₂ microspheres was also investigated.     

Multi-layered mesh-like MoS2 hierarchical nanostructure fabricated on Ti foil: An efficient noble metal-free photocatalyst for visible-light-driven H2 evolution from water

In the present work, multi-layered mesh-like MoS₂ hierarchical nanostructure was fabricated on a Ti foil in a hydrothermal process. Meanwhile, photocatalytic H₂ evolution from water over the as-prepared MoS₂ hierarchical nanostructure was investigated under visible irradiation. The results indicate that the as-prepared MoS₂ hierarchical nanostructure consists of the vertically grown few-layers MoS₂ nanosheets. And this three-dimensional mesh-like MoS₂ hierarchical nanostructure possesses high photocatalytic activity for visible-light-driven H₂ evolution from water. A rate of H₂ evolution of approximately 240 μmol g^− 1 h^− 1 was achieved under optimal conditions. Furthermore, the photocatalytic mechanism was preliminarily discussed.     

Microwave-assisted synthesis of Ag–TiO2/graphene composite for hydrogen production under visible light irradiation

Novel photocatalysts based on silver (Ag), TiO₂, and graphene were successfully synthesized by microwave-assisted hydrothermal method. The prepared photocatalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The influence of silver loading and graphene incorporation on photocatalytic hydrogen (H₂) production of as-prepared samples was investigated in methanolic aqueous solution under visible light irradiation (λ≥420 nm). The results showed that Ag–TiO₂/graphene composite had appreciably enhanced photocatalytic H₂ production performance under visible light illumination compared to pure TiO₂, Ag–TiO₂ and TiO₂/graphene samples. The enhanced photocatalytic hydrogen production activity of Ag–TiO₂/graphene composite under visible light irradiation could be attributed to increased visible light absorption, reduced recombination of photogenerated charge carriers and high specific surface area. This novel study provides more insight for the development of novel visible light responsive TiO²⁻ graphene based photocatalysts for energy applications.     

SnS2/TiO2 nanocomposites with enhanced visible light-driven photoreduction of aqueous Cr(VI)

SnS₂/TiO₂ nanocomposites have been synthesized via microwave assisted hydrothermal treatment of tetrabutyl titanate in the presence of SnS₂ nanoplates in the solvent of ethanol at 160 °C for 1 h. The physical and chemical properties of SnS₂/TiO₂ were studied by XRD, FESEM, EDS, TEM, XPS and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activity of SnS₂/TiO₂ nanocomposites were evaluated by photoreduction of aqueous Cr(VI) under visible light (λ>420 nm) irradiation. The experimental results showed that the SnS₂/TiO₂ nanocomposites exhibited excellent reduction efficiency of Cr(VI) (~87%) than that of pure TiO₂ and SnS₂. The SnS₂/TiO₂ nanocomposites were expected to be a promising candidate as effective photocatalysts in the treatment of Cr(VI) wastewater.