甲醇在纳米TiO_2作用下进行光催化氧化反应的机理研究

以纳米TiO2 为催化剂 ,以主波长为 36 4nm的汞灯为光源 ,用气相色谱法分别考察了 0 .1mol/L的甲醇、甲醛和甲酸水溶液进行光催化氧化反应的动力学规律 .Langmuir Hinshelwood方程进行核算结果证明 ,该组反应均为零级反应 .用TEM、XRD、SSA和XPS对催化剂进行表征 .根据XPS的检测结果提出了甲醇光催化氧化的反应机理 .TiO2 光激发活化时间约为 30～ 6 0min ,生成物及剩余反应物浓度随时间变化的曲线表明 ,该反应速率为HCH2 OH <HCHO <HCOOH ,XPS法检测到了反应的中间产物 ,可推断出HCH2 OH的氧化步骤 .

Dual-channel redox reactions for photocatalytic H_(2)-evolution coupled with photoreforming oxidation of waste materials

Dual-channel redox reaction system is advantageous for photocatalytic hydrogen(H_(2))production when coupled with photoreforming oxidation of waste materials,benefiting both thermodynamically and kinetically.However,existing reviews primarily focus on specific oxidation reactions,such as oxidative organic synthesis and water remediation,often neglecting recent advancements in plastic upgrading,biomass conversion,and H_(2)O_(2)production,and failing to provide an in-depth discussion of catalytic mechanisms.This review addresses these gaps by offering a comprehensive overview of recent advancements in dual-channel redox reactions for photocatalytic H_(2)-evolution and waste photoreforming.It highlights waste-to-wealth design concepts,examines the challenges,advantages and diverse applications of dual-channel photocatalytic reactions,including photoreforming of biomass,alcohol,amine,plastic waste,organic pollutants,and H_(2)O_(2)production.Emphasizing improvement strategies and exploration of catalytic mechanisms,it includes advanced in-situ characterization,spin capture experiments,and DFT calculations.By identifying challenges and future directions in this field,this review provides valuable insights for designing innovative dual-channel photocatalytic systems.

Self-assembled S-scheme In_(2.77)S_(4)/K^(+)-doped g-C_(3)N_(4)photocatalyst with selective O_(2) reduction pathway for efficient H_(2)O_(2) production using water and air

The development of an efficient artificial H_(2)O_(2) photosynthesis system is a challenging work using H_(2)O and O_(2) as starting materials.Herein,3D In_(2.77)S_(4) nanoflower precursor was in-situ deposited on K^(+)-doped g-C_(3)N_(4)(KCN)nanosheets using a solvothermal method,then In_(2.77)S_(4)/KCN(IS/KCN)het-erojunction with an intimate interface was obtained after a calcination process.The investigation shows that the photocatalytic H_(2)O_(2) production rate of 50IS/KCN can reach up to 1.36 mmol g^(-1)h^(-1)without any sacrificial reagents under visible light irradiation,which is 9.2 times and 4.1 times higher than that of KCN and In_(2.77)S_(4)/respectively.The enhanced activity of the above composite can be mainly attributed to the S-scheme charge transfer route between KCN and In_(2.77)S_(4) according to density functional theory calculations,electron paramagnetic resonance and free radical capture tests,leading to an expanded light response range and rapid charge separation at their interface,as well as preserving the active electrons and holes for H_(2)O_(2) production.Besides,the unique 3D nanostructure and surface hydrophobicity of IS/KCN facilitate the diffusion and transportation of O_(2) around the active centers,the energy barriers of O_(2) protonation and H_(2)O_(2) desorption steps are ef-fectively reduced over the composite.In addition,this system also exhibits excellent light harvesting ability and stability.This work provides a potential strategy to explore a sustainable H_(2)O_(2) photo-synthesis pathway through the design of heterojunctions with intimate interfaces and desired reac-tion thermodynamics and kinetics.

Dipole polarization modulating of vinylene-linked covalent organic frameworks for efficient photocatalytic hydrogen evolution

Photocatalytic hydrogen(H_(2))evolution using covalent organic frameworks(COFs)is an attractive and promising avenue for exploration,but one of its big challenges is low photo-induced charge separation.In this study,we present a straightforward and facile dipole polarization engineering strategy to enhance charge separation efficiency,achieved through atomic modulation(O,S,and Se)of the COF monomer.Our findings demonstrate that incorporating atoms with varying electronegativities into the COF matrix significantly influences the local dipole moment,thereby affecting charge separation efficiency and photostability,which in turn affects the rates of photocatalytic H_(2) evolution.As a result,the newly developed TMT-BO-COF,which contains highly electronegative O atoms,exhibits the lowest exciton binding energy,the highest efficiency in charge separation and transportation,and the longest lifetime of the active charges.This leads to an impressive average H_(2) production rate of 23.7 mmol g^(−1) h^(−1),which is 2.5 and 24.5 times higher than that of TMT-BS-COF(containing S atoms)and TMT-BSe-COF(containing Se atoms),respectively.A novel photocatalytic hydrogen evolution mechanism based on proton-coupled electron transfer on N in the structure of triazine rings in vinylene-linked COFs is proposed by theoretical calculations.Our findings provide new insights into the design of highly photoactive organic framework materials for H_(2) evolution and beyond.

In-situ photodeposition of co-catalyst Ni_(2)P on CdS for photocatalytic conversion of ethanol for synergistic hydrogen production

In this study,Ni_(2)P/CdS composites were constructed by depositing non-precious metal co-catalyst Ni_(2)P on a one-dimensional network of CdS using a simple in-situ photodeposition method.The prepared photocatalysts promoted the decomposition of ethanol into high-value-added products while generating hydrogen.The composite photoanodes loaded with the Ni_(2)P co-catalysts showed significantly higher ethanol conversion and hydrogen production in the visible light region,which was almost three times higher than that of pure CdS.The main products of photocatalytic ethanol production are acetaldehyde(AA)and 2,3-butanediol(2,3-BDA).Compared with CdS,the selectivity of the composite photocatalysts for converting ethanol to acetaldehyde was significantly improved(62% to 78%).Characterization of the prepared photocatalysts confirmed that the loading of Ni_(2)P co-catalysts on CdS not only broadened the optical region of the catalysts for trapping light but also effectively promoted the separation and transfer of charge carriers,which significantly improved the photocatalytic efficiency of ethanol conversion and hydrogen production in the catalysts.It has been proven through Electron Paramagnetic Resonance testing that loading a Ni_(2)P co-catalyst on CdS is beneficial for the adsorption of hydroxyethyl radicals(*CH(OH)CH_(3)),thereby further improving the selectivity of acetaldehyde.This study plays an important role in the rational design of composite catalyst structures and the introduction of co-catalysts to improve catalyst performance,promote green chemistry,advocate a low-carbon society,and promote sustainable development.

Facile synthesis and enhanced photocatalytic H_2-evolution performance of NiS_2-modified g-C_3N_4 photocatalysts

NiS2 is a promising cocatalyst to improve the photocatalytic performance of g-C3N4 for the production of H2.However,the synthesis of the NiS2 cocatalyst usually requires harsh conditions,which risks destroying the microstructures of the g-C3N4 photocatalysts.In this study,a facile and low-temperature（80 ℃） impregnation method was developed to prepare NiS2/g-C3N4 photocatalysts.First,the g-C3N4 powders were processed by the hydrothermal method in order to introduce oxygen-containing functional groups（such as-OH and-C0NH-） to the surface of g-C3N4.Then,the Ni^2＋ ions could be adsorbed near the g-C3N4 via strong electrostatic interaction between g-C3N4 and Ni^2＋ ions upon the addition of Ni（NO3）2 solution.Finally,NiS2 nanoparticles were formed on the surface of g-C3N4 upon the addition of TAA.It was found that the NiS2 nanoparticles were solidly and homogeneously grafted on the surface of g-C3N4,resulting in greatly improved photocatalytic H2production.When the amount of NiS2 was 3 wt%,the resultant NiS2/g-C3N4 photocatalyst showed the highest H2 evolution rate（116.343 μmol h^-1 g^-1）,which is significantly higher than that of the pure g-C3N4（3 μmol h^-1 g^-1）.Moreover,the results of a recycling test for the NiS2/g-C3N4（3 wt%）sample showed that this sample could maintain a stable and effective photocatalytic H2-evolution performance under visible-light irradiation.Based on the above results,a possible mechanism of the improved photocatalytic performance was proposed for the presented NiS2/g-C3N4 photocatalysts,in which the photogenerated electrons of g-C3N4 can be rapidly transferred to the NiS2 nanoparticles via the close and continuous contact between them;then,the photogenerated electrons rapidly react with H2O adsorbed on the surface of NiS2,which has a surficial metallic character and high catalytic activity,to produce H2.Considering the mild and facile synthesis method,the presented low-cost and highly efficient NiS2-modified g-C3N4 photocatalysts would have great potential for practical use in photocatalytic H2 production.

Enhanced visible light photocatalytic H_2 production over Z-scheme g-C_3N_4 nansheets/WO_3 nanorods nanocomposites loaded with Ni(OH)_x cocatalysts

Novel WO3/g-C3N4/Ni（OH）x hybrids have been successfully synthesized by a two-step strategy of high temperature calcination and in situ photodeposition.Their photocatalytic performance was investigated using TEOA as a hole scavenger under visible light irradiation.The loading of WO3 and Ni（OH）x cocatalysts boosted the photocatalytic H2 evolution efficiency of g-C3N4.WO3/g-C3N4/Ni（OH）x with 20 wt%defective WO3 and 4.8 wt%Ni（OH）x showed the highest hydrogen production rate of 576 μmol/（g·h）,which was 5.7,10.8 and 230 times higher than those of g-C3N4/4.8 wt%Ni（OH）x,20 wt%WO3/C3N4 and g-C3N4 photocatalysts,respectively.The remarkably enhanced H2 evolution performance was ascribed to the combination effects of the Z-scheme heterojunction（WO3/g-C3N4） and loaded cocatalysts（Ni（OH）x）,which effectively inhibited the recombination of the photoexcited electron-hole pairs of g-C3N4 and improved both H2 evolution and TEOA oxidation kinetics.The electron spin resonance spectra of ·O2^- and ·OH radicals provided evidence for the Z-scheme charge separation mechanism.The loading of easily available Ni（OH）x cocatalysts on the Z-scheme WO3/g-C3N4 nanocomposites provided insights into constructing a robust multiple-heterojunction material for photocatalytic applications.

Preparation of ZnO Nanoparticles and Photocatalytic H2 Production Activity from Different Sacrificial Reagent Solutions

ZnO nanoparticles were synthesized via a direct precipitation method followed by a hetero- geneous azeotropic distillation and calcination processes, and then characterized by X-ray power diffraction, scanning electron microscopy, transmission electron microscopy, and ni- trogen adsorption-desorption measurement. The effects of Pt-loading amount, calcination temperature, and sacrificial reagents on the present ZnO suspension were investigated, photocatalytic H2 evolution efficiency from the The experimental results indicate that ZnO rianoparticles calcined at 400℃ exhibit the best photoactivity for the H2 production in comparison with the samples calcined at 300 and 500℃, and the photoeatalytie H2 production efficiency from a methanol solution is much higher than that from a triethanolamine solution. It can be ascribed to the oxidization of methanol also contributes to the H2 production during the photochemical reaction process. Moreover, the photocatalytic mechanism for the H2 production from the present ZnO suspension system containing methanol solution is also discussed in detail.

Sulfurization synthesis and photocatalytic activity of oxysulfide La_3NbS_2O_5

The oxysulfide La3NbS2O5 was synthesized by sulfurization using H2S and characterized by X-ray diffraction （XRD）, UV-Vis diffuse reflectance spectroscopy （DRS） and field emission scanning electron microscopy （FE-SEM）. The relationship between the sulfurization conditions and the photocatalytic activities for H2 evolution was investigated. Sulfurization method allowed for synthesis of La3NbS2O5 at much lower temperatures and significantly shortened reaction time of 1 h compared with conventional solid-state techniques. The particle morphologies were regular platelike with sizes of 0.1-0.6μm and smooth surfaces. The highest activity for H2 evolution was obtained at 1073 K for 1 h, which was about 1.83 times that of La3NbS2O5 prepared by solid-state method.

Hydrogenation and Ammoniation of SrTiO3 for an Enhanced Visible-light Photocatalysis

Hydrogenation and ammoniation of SrTiOa （STO）, a normal ultraviolet photocatalyst, were performed by annealing STO（100） in Hz：N2=5%：95% and NH3, respectively, at various temperatures T. It was found that hydrogenation at T≥900℃ remarkably enhanced the UV photocatalytic ability of STO, but the visible-light photocatalysis was still unavailable, while ammoniation at T≥800℃ introduced the N doping, resulting in visible-light photocat- alytie activity. Furthermore, when a hydrogenated STO was subjected to ammoniation, the visible-light photocatalytie ability was nearly the same as that of the ammoniated one; but the hydrogenation of an ammoniated one significantly enhanced visible-light photoeatalysis, indicating a synergetic effect of hydrogenation and ammoniation. Discussions and identifications have been made to analyze these results.

Thermal nitridation of triazine motifs to heptazine-based carbon nitride frameworks for use in visible light photocatalysis

A thermal nitridation route for the assembly and polymerization of molecular triazine units to heptazine-based covalent frameworks has been successfully established. The obtained conjugated carbon nitride polymers feature nanostructures that show enhanced photocatalytic reactivity for hydrogen production under visible light irradiation.

Octahedral Cu_2O-modified TiO_2 nanotube arrays for efficient photocatalytic reduction of CO_2

A photocatalyst composed of TiO 2 nanotube arrays（TNTs） and octahedral Cu2 O nanoparticles was fabricated,and its performance in the photocatalytic reduction of CO2 under visible and simulated solar irradiation was studied. The average nanotube diameter and length was 100 nm and 5 μm,respectively. The different amount of octahedral Cu2 O modified TNTs were obtained by varying electrochemical deposition time. TNTs modified with an optimized amount of Cu2 O nanoparticles exhibited high efficiency in the photocatalysis,and the predominant hydrocarbon product was methane. The methane yield increased with increasing Cu2 O content of the catalyst up to a certain deposition time,and decreased with further increase in Cu2 O deposition time. Insufficient deposition time（5 min） resulted in a small amount of Cu2 O nanoparticles on the TNTs,leading to the disadvantage of harvesting light. However,excess deposition time（45 min） gave rise to entire TNT surface being most covered with Cu2 O nanoparticles with large sizes,inconvenient for the transport of photo-generated carriers. The highest methane yield under simulated solar and visible light irradiation was observed for the catalysts prepared at a Cu2 O deposition time of 15 and 30 min respectively. The morphology,crystallization,photoresponse and electrochemical properties of the catalyst were characterized to understand the mechanism of its high photocatalytic activity. The TNT structure provided abundant active sites for the adsorption of reactants,and promoted the transport of photogenerated carriers that improved charge separation. Modifying the TNTs with octahedral Cu2 O nanoparticles promoted light absorption,and prevented the hydrocarbon product from oxidation. These factors provided the Cu2O-modified TNT photocatalyst with high efficiency in the reduction of CO2,without requiring co-catalysts or sacrificial agents.

Enhanced photocatalytic hydrogen generation of mesoporous rutile TiO_2 single crystal with wholly exposed {111} facets

The development of semiconductor photocatalysts with highly reactive facets exposed has great potential to improve their photocatalytic reactivity. We report the synthesis of mesoporous rutile TiO 2 single crystals with tunable ratios of {110} and {111} facets through the seeded-template hydrothermal method. With increasing the amount of morphology controlling agent NaF,the facet ratio of {111} to {110} increases,and eventually the mesoporous rutile TiO 2 single crystals with wholly exposed {111} reactive facets are obtained. The resultant faceted mesoporous single crystals exhibit a superior photocatalytic performance of hydrogen evolution to mesoporous single crystals with a large percentage of thermodynamically stable {110} facets,as well as the solid rutile single crystals. ？ 2015,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.

Highly crystalline carbon nitride hollow spheres with enhanced photocatalytic performance

Graphitic carbon nitride(g-C_(3)N_(4))has emerged as a remarkably promising photocatalyst for addressing environmental and energy issues;however,it exhibits only moderate photocatalytic activity because of its low specific surface area and high recombination of carriers.Preparation of crystalline g-C_(3)N_(4) by the molten salt method has proven to be an effective method to improve the photocatalytic activity.However,crystalline g-C_(3)N_(4) prepared by the conventional molten salt method exhibits a less regular morphology.Herein,highly crystalline g-C_(3)N_(4) hollow spheres(CCNHS)were successfully prepared by the molten salt method using cyanuric acid-melamine as a precursor.The higher crystallization of the CCNHS samples not only repaired the structural defects at the surface of the CCNHS samples but also established a built-in electric field between heptazine-based g-C_(3)N_(4) and triazine-based g-C_(3)N_(4).The hollow structure improved the level of light energy utilization and increased the number of active sites for photocatalytic reactions.Because of the above characteristics,the as-prepared CCNHS samples simultaneously realized photocatalytic hydrogen evolution with the degradation of the plasticizer bisphenol A.This research offers a new perspective on the structural optimization of supramolecular self-assembly.

CdS-modified one-dimensional g-C_3N_4 porous nanotubes for efficient visible-light photocatalytic conversion

A heterojunction photocatalyst based on porous tubular g-C3N4 decorated with CdS nanoparticles was fabricated by a facile hydrothermal co-deposition method.The one-dimensional porous structure of g-C3N4 provides a higher specific surface area,enhanced light absorption,and better separation and transport performance of charge carriers along the longitudinal direction,all of which synergistically contribute to the superior photocatalytic activity observed.The significantly enhanced catalytic efficiency is also a benefit originating from the fast transfer of photogenerated electrons and holes between g-C3N4 and CdS through a built-in electric field,which was confirmed by investigating the morphology,structure,optical properties,electrochemical properties,and photocatalytic activities.Photocatalytic degradation of rhodamine B(RhB)and photocatalytic hydrogen evolution reaction were also carried out to investigate its photocatalytic performance.RhB can be degraded completely within 60 min,and the optimum H2 evolution rate of tubular g-C3N4/CdS composite is as high as 71.6μmol h^–1,which is about 16.3 times higher than that of pure bulk g-C3N4.The as-prepared nanostructure would be suitable for treating environmental pollutants as well as for water splitting.

Enhanced photocatalytic H_2 production over dual-cocatalyst-modified g-C_3N_4 heterojunctions

Ag nanoparticles (NPs) were deposited on the surface of g-C3N4 (CN) by an in situ calcination method. NiS was successfully loaded onto the composites by a hydrothermal method. The results showed that the 10 wt%-NiS/1.0 wt%-Ag/CN composite exhibits excellent photocatalytic H2 generation performance under solar-light irradiation. An H2 production rate of 9.728 mmol·g^-1·h^-1 was achieved, which is 10.82-, 3.45-, and 2.77-times higher than those of pure g-C3N4, 10 wt%-NiS/CN, and 1.0 wt%-Ag/CN composites, respectively. This enhanced photocatalytic H2 generation can be ascribed to the co-decoration of Ag and NiS on the surface of g-C3N4, which efficiently improves light harvesting capacity, photogenerated charge carrier separation, and photocatalytic H2 production kinetics. Thus, this study demonstrates an effective strategy for constructing excellent g-C3N4-related composite photocatalysts for H2 production by using different co-catalysts.

The roles and mechanism of cocatalysts in photocatalytic water splitting to produce hydrogen

Photocatalytic hydrogen(H2)evolution via water spilling over semiconductors has been considered to be one of the most promising strategies for sustainable energy supply in the future to provide non-pollution and renewable energy.The key to efficient conversion of solar-chemical energy is the design of an efficient structure for high charge separation and transportation.Therefore,cocatalysts are necessary in boosting photocatalytic H2 evolution.To date,semiconductor photocatalysts have been modified by various cocatalysts due to the extended light harvest,enhanced charge carrier separation efficiency and improved stability.This review focuses on recent developments of cocatalysts in photocatalytic H2 evolution,the roles and mechanism of the cocatalysts are discussed in detail.The cocatalysts can be divided into the following categories:metal/alloy cocatalysts,metal phosphides cocatalysts,metal oxide/hydroxide cocatalysts,carbon-based cocatalysts,dual cocatalysts,Z-scheme cocatalysts and MOFs cocatalysts.The future research and forecast for photocatalytic hydrogen generation are also suggested.

Ti_(3)C_(2) MXene co-catalyst assembled with mesoporous TiO_(2) for boosting photocatalytic activity of methyl orange degradation and hydrogen production

Photocatalytic degradation and hydrogen production using solar energy through semiconductor photocatalysts are deemed to be a powerful approach for solving environmental and energy crisis.However,the biggest challenge in photocatalysis is the efficient separation of photo-induced carriers.To this end,we report that the mesoporous TiO_(2)nanoparticles are anchored on highly conductive Ti_(3)C_(2)MXene co-catalyst by electrostatic self-assembly strategy.The constructed mesoporous TiO_(2)/Ti_(3)C_(2)composites display that the mesoporous TiO_(2)nanoparticles are uniformly distributed on the surface of layer structured Ti_(3)C_(2)nanosheets.More importantly,the as-obtained mesoporous TiO_(2)/Ti_(3)C_(2)composites reveal the significantly enhanced light absorption performance,photo-induced carriers separation and transfer ability,thus boosting the photocatalytic activity.The photocatalytic methyl orange degradation efficiency of mesoporous TiO_(2)/Ti_(3)C_(2)composite with an optimized Ti_(3)C_(2)content(3 wt%)can reach 99.6%within 40 min.The capture experiments of active species confirm that the·O_(2)-and·OH play major role in photocatalytic degradation process.Furthermore,the optimized mesoporous TiO_(2)/Ti_(3)C_(2)composite also shows an excellent photocatalytic H2 production rate of 218.85μmol g^(-1)h^(-1),resulting in a 5.6 times activity as compared with the pristine mesoporous TiO_(2)nanoparticles.This study demonstrates that the MXene family materials can be applied as highly efficient noble-metal-free co-catalysts in the field of photocatalysis.

Accelerating photocatalytic hydrogen evolution and pollutant degradation by coupling organic co-catalysts with TiO_2

Accelerating the separation efficiency of photoexcited electron-hole pairs with the help of highly active co-catalysts has proven to be a promising approach for improving photocatalytic activity. Thus far, the most developed co-catalysts for semiconductor-based photocatalysis are inorganic materials;the employment of a specific organic molecule as a co-catalyst for photocatalytic hydrogen evolution and pollutant photodegradation is rare and still remains a challenging task. Herein, we report on the use of an organic molecule, oxamide (OA), as a novel co-catalyst to enhance electron- hole separation, photocatalytic H2 evolution, and dye degradation over TiO2 nanosheets. OA-modified TiO2 samples were prepared by a wet chemical route and demonstrated improved light absorption in the visible-light region and more efficient charge transport. The photocatalytic performance of H2 evolution from water splitting and rhodamine B (RhB) degradation for an optimal OA-modified TiO2 photocatalyst reached 2.37 mmol g^–1 h^–1 and 1.43 × 10^-2 min^-1, respectively, which were 2.4 and 3.8 times higher than those of pristine TiO2, respectively. A possible mechanism is proposed, in which the specific π-conjugated structure of OA is suggested to play a key role in the enhancement of the charge transfer and catalytic capability of TiO2. This work may provide advanced insight into the development of a variety of metal-free organic molecules as functional co-catalysts for improved solar-to-fuel conversion and environmental remediation.

Ultrafine metal nanoparticles loaded on TiO_2 nanorods:Synthesis strategy and photocatalytic activity

Ultrafine noble metal nanoparticles （Pt, Pd, or Au） co-catalyst loaded on the surface of rutile and brookite TiO2 were prepared via a simple photo-deposition strategy under high vacuum conditions. The properties of the prepared samples were determined by different characterization techniques, including X-ray diffraction, transmission electron microscopy, diffuse reflectance ultraviolet-visible spectroscopy, and photoluminescence spectroscopy. The photocatalytic performance of the samples was evaluated by monitoring the reforming of methanol. Co-catalyst loading greatly improved the photocatalytic activity of TiO2. Specifically, Pt-TiO2 displayed the highest photocatalytic activity among all samples studied, followed by Pd-TiO2 and then Au-TiO2. Furthermore, this photocatalytic behavior was not influenced by the intrinsic nature of the TiO2 semiconductor photocatalyst. Similar photocatalytic activity trends were achieved with both sets of noble metal-loaded photocatalysts prepared using rutile and brookite TiO2 as supports. By examining the physicochemical and photocatalytic properties, the factors controlling the photocatalytic activity of the noble metal-loaded TiO2 samples were discussed in detail.