Air-condition process for scalable fabrication of CdS/ZnS 1D/2D heterojunctions toward efficient and stable photocatalytic hydrogen production

We report the scalable fabrication of CdS/ZnS 1D/2D heterojunctions under ambient air conditions(i.e.,room temperature and atmospheric pressure)in which ZnS nanoparticles are anchored on the surface of CdS nanosheets.The as-formed heterojunctions exhibit a significantly enhanced photocatalytic H_(2) evolution rate of 14.02 mmol h^(-1) g^(-1) when irradiated with visible light,which is~10 and 85 times higher than those of pristine CdS nanosheets and CdS nanoparticles,respectively,and superior to most of the CdS-based photocatalysts reported to date.Furthermore,they provide robust photocatalytic performance with demonstratable stability over 58 h,indicating their potential for practical applications.The formation of 1D/2D heterojunctions not only provides improved exposed active sites that respond to illumination but also provides a rapid pathway to generate photogenerated carriers for efficient separation and transfer through the matrix of single-crystalline CdS nanosheets.In addition,first-principles simulations demonstrate that the existence of rich Zn vacancies increases the energy level of the ZnS valence band maximum to construct type-II and Z-scheme mixed heterojunctions,which plays a critical role in suppressing the recombination of carriers with limited photocorrosion of CdS to enhance photocatalytic behavior.

In situ construction of protonated g-C3N4/Ti3C2 MXene Schottky heterojunctions for efficient photocatalytic hydrogen production

Converting sustainable solar energy into hydrogen energy over semiconductor-based photocatalytic materials provides an alternative to fossil fuel consumption.However,efficient photocatalytic splitting of water to realize carbon-free hydrogen production remains a challenge.Heterojunction photocatalysts with well-defined dimensionality and perfectly matched interfaces are promising for achieving highly efficient solar-to-hydrogen conversion.Herein,we report the fabrication of a novel type of protonated graphitic carbon nitride(PCN)/Ti3C2 MXene heterojunctions with strong interfacial interactions.As expected,the two-dimensional(2D)PCN/2D Ti3C2 MXene interface heterojunction achieves a highly improved hydrogen evolution rate(2181μmol∙g‒1)in comparison with bulk g-C3N4(393μmol∙g‒1)and protonated g-C3N4(816μmol∙g‒1).The charge-regulated surfaces of PCN and the accelerated charge transport at the face-to-face 2D/2D Schottky heterojunction interface are the major contributors to the excellent hydrogen evolution performance of the composite photocatalyst.

Nanoheterostructured photocatalysts for improving photocatalytic hydrogen production

Rapid industrialization has accordingly increased the demand for energy.This has resulted in the increasingly severe energy and environmental crises.Hydrogen production,based on the photocatalytic water splitting driven by sunlight,is able to directly convert solar energy into a usable or storable energy resource,which is considered to be an ideal alternative energy source to assist in solving the energy crisis and environmental pollution.Unfortunately,the hydrogen production efficiency of single phase photocatalysts is too low to meet the practical requirements.The construction of heterostructured photocatalyst systems,which are comprised of multiple components or multiple phases,is an efficient method to facilitate the separation of electron‐hole pairs to minimize the energy‐waste,provide more electrons,enhance their redox ability,and hence improve the photocatalytic activity.We summarize the recent progress in the rational design and fabrication of nanoheterostructured photocatalysts.The heterojunction photocatalytic hydrogen generation systems can be divided into type‐I,type‐II,pn‐junction and Z‐scheme junction,according to the differences in the transfer of the photogenerated electrons and holes.Finally,a summary and some of the challenges and prospects for the future development of heterojunction photocatalytic systems are discussed.

3D flower-like heterostructured TiO_2@Ni(OH)_2 microspheres for solar photocatalytic hydrogen production

TiO2@Ni(OH)2 core-shell microspheres were synthesized by a facile strategy to obtain a perfect 3D flower-like nanostructure with well-arranged Ni(OH)2 nanoflakes on the surfaces of TiO2 microspheres;this arrangement led to a six-fold enhancement in photocatalytic hydrogen evolution. The unique p-n type heterostructure not only promotes the separation and transfer of photogenerated charge carriers significantly, but also offers more active sites for photocatalytic hydrogen production. A photocatalytic mechanism is proposed based on the results of electrochemical measurements and X-ray photoelectron spectroscopy.

Biomolecule-assisted, cost-effective synthesis of a Zn_(0.9)Cd_(0.1)S solid solution for efficient photocatalytic hydrogen production under visible light

A series of alloyed Zn‐Cd‐S solid solutions with a cubic zinc blende structure were fabricated hydrothermally with the assistance of L‐cystine under mild conditions.The products were characterized by XRD,TEM,HRTEM,XPS,UV‐vis,and BET techniques,and the photocatalytic performance for the reduction of water to H2on the solid solutions was evaluated in the presence of S2?/SO32?as hole scavengers under visible light illumination.Among all the samples,the highest photocatalytic activity was achieved over Zn0.9Cd0.1S with a rate of4.4mmol h?1g?1,even without a co‐catalyst,which far exceeded that of CdS.Moreover,Zn0.9Cd0.1S displayed excellent anti‐photocorrosion properties during the photoreduction of water into H2.The enhancement in the photocatalytic performance was mainly attributed to the efficient charge transfer in the Zn0.9Cd0.1alloyed structure and the high surface area.This work provides a simple,cost‐effective and green technique,which can be generalized as a rational preparation route for the large‐scale fabrication of metal sulfide photocatalysts.

Rationally construction of atomic-precise interfacial charge transfer channel and strong build-in electric field in nanocluster-based Zscheme heterojunctions with enhanced photocatalytic hydrogen production

The lack of effective charge transfer driving force and channel limits the electron directional migration in nanoclusters(NC)-based heterostructures,resulting in poor photocatalytic performance.Herein,a Z-scheme NC-based heterojunction(Pt1Ag28-BTT/CoP,BTT=1,3,5-benzenetrithiol)with strong internal electric field is constructed via interfacial Co-S bond,which exhibits an absolutely superiority in photocatalytic performance with 24.89 mmol·h^(−1)·g−1 H_(2)production rate,25.77%apparent quantum yield at 420 nm,and~100%activity retention in stability,compared with Pt1Ag28-BDT/CoP(BDT=1,3-benzenedithiol),Ag29-BDT/CoP,and CoP.The enhanced catalytic performance is contributed by the dual modulation strategy of inner core and outer shell of NC,wherein,the center Pt single atom doping regulates the band structure of NC to match well with CoP,builds internal electric field,and then drives photogenerated electrons steering;the accurate surface S modification promotes the formation of Co-S atomic-precise interface channel for further high-efficient Z-scheme charge directional migration.This work opens a new avenue for designing NC-based heterojunction with matchable band structure and valid interfacial charge transfer.

Progress in manipulating spin polarization for solar hydrogen production

Photocatalytic and photoelectrochemical water splitting using semiconductor materials are effective approaches for converting solar energy into hydrogen fuel.In the past few years,a series of photocatalysts/photoelectrocatalysts have been developed and optimized to achieve efficient solar hydrogen production.Among various optimization strategies,the regulation of spin polarization can tailor the intrinsic optoelectronic properties for retarding charge recombination and enhancing surface reactions,thus improving the solar-to-hydrogen(STH)efficiency.This review presents recent advances in the regulation of spin polarization to enhance spin polarized-dependent solar hydrogen evolution activity.Specifically,spin polarization manipulation strategies of several typical photocatalysts/photoelectrocatalysts(e.g.,metallic oxides,metallic sulfides,non-metallic semiconductors,ferroelectric materials,and chiral molecules)are described.In the end,the critical challenges and perspectives of spin polarization regulation towards future solar energy conversion are briefly provided.

In-MOF-derived In_(2)S_(3)/Bi_(2)S_(3) heterojunction for enhanced photocatalytic hydrogen production

Transition metal sulfides are commonly studied as photocatalysts for water splitting in solar-to-fuel conversion.However,the effectiveness of these photoca-talysts is limited by the recombination and restricted light absorption capacity of carriers.In this paper,a broad spectrum responsive In_(2)S_(3)/Bi_(2)S_(3)heterojunction is cons-tructed by in-situ integrating Bi_(2)S_(3)with the In_(2)S_(3),derived from an In-MOF precursor,via the high-temperature sulfidation and solvothermal methods.Benefiting from the synergistic effect of wide-spectrum response,effective charge separation and transfer,and strong heterogeneous interfacial contacts,the In_(2)S_(3)/Bi_(2)S_(3)heterojunction demons-trates a rate of 0.71 mmol/(g∙h),which is 2.2 and 1.7 times as much as those of In_(2)S_(3)(0.32 mmol/(g∙h))and Bi_(2)S_(3)(0.41 mmol/(g∙h)),respectively.This paper provides a novel idea for rationally designing innovative heterojunc-tion photocatalysts of transition metal sulfides for photocatalytic hydrogen production.

Facile preparation of self-assembled MXene@Au@CdS nanocomposite with enhanced photocatalytic hydrogen production activity

Photocatalytic hydrogen production is considered a promising approach to generating clean sustainable energy.However,the conventional co-catalyst(e.g.,Pt)used in photocatalytic hydrogen production is high-cost and difficult to obtain.Here,we designed and prepared a ternary nanocomposite MXene@Au@Cd S,which can be used in the field of efficient and excellent photocatalytic hydrogen production.The MXene@Au@Cd S has a hydrogen production rate of 17,070.43μmol g^-1h^-1(tested for 2 h),which is 1.85 times that of pure Cd S nanomaterials.The improved hydrogen production performance of the MXene@Au@Cd S is attributed to:(i)MXene provides more active adsorption sites and reaction centers for Au and Cd S nanoparticles;(ii)the synergistic effect of Au’s strong surface plasmon resonance expands the optical response range of Cd S.Therefore,this work solves the problem of the solid connection between the surface functional groups of photocatalyst,and achieves rapid interface charge transfer and long-term stability during the hydrogen production.

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.

Boosting photocatalytic hydrogen production by creating isotype heterojunctions and single-atom active sites in highly-crystallized carbon nitride

Carbon nitride-based photocatalysts hold an enormous potential in producing hydrogen.A strategy to simultaneously create isotype heterojunctions and active sites in highly-crystallized carbon nitride is anticipated to significantly boost the photocatalytic activity,but is yet to be realized.Herein,we find that cobalt salt added in the ionothermal synthesis can promote the phase transition of heptazine-based crystalline carbon nitride(CCN)to triazine-based poly(triazine imide)(PTI),rendering the creation of singleatom cobalt coordinated isotype CCN/PTI heterojunction.Co-CCN/PTI exhibits an appreciable apparent quantum yield of 20.88%at 425 nm for photocatalytic hydrogen production with a rate achieving3538μmol h^(-1)g^(-1)(λ>420 nm),which is 4.8 times that of CCN and 27.6 times that of PTI.The high photocatalytic activity is attributed to the Type II isotype highly-crystallized CCN/PTI heterojunction for promoting charge carrier migration,and the single-atom Co sites for accelerating surface oxidation reaction.

Facile construction of highly efficient MOF-based Pd@UiO-66-NH_(2)@ZnIn_(2)S_(4)flower-like nanocomposites for visible-light-driven photocatalytic hydrogen production

Construction of metal-organic-frame works-based composite photocatalysts has attracted much attention for the reasonable band gap and high surface areas to improve the photocatalytic activity.In this study,the ternary heterojunction Pd@UiO-66-NH_(2)@ZnIn_(2)S_(4)nanocomposites were facilely prepared for the first time by a two-step method.The visible-light-promoted hydrogen production rate of 0.3%Pd@UiO-66-NH_(2)@ZnIn_(2)S_(4)reaches up to 5.26 mmol g^(-1)h^(-1),which is evidently much higher than pure UiO-66-NH_(2),ZnIn_(2)S_(4)and binary UiO-66-NH_(2)/ZnIn_(2)S_(4)composites.Such a huge improvement in the photocatalytic performance is mainly attributed to the matched band gap of ZnIn_(2)S_(4)and UiO-66-NH_(2),and the introduction of Pd NPs into photocatalysts that broaden spectral response range and promote the photon induced charge carrier separation.This work may provide a feasible approach for the design and construction of metal-organic-frameworks-based photocatalytic materials.

Performance and Mechanism Research of Au-HSTiO2 on Photocatalytic Hydrogen Production

In this paper,we report our attempts to raise the efficiency of liquid reduction method when using high specific surface area TiO2(HSTiO2)by doping Au.Characterization of Au-HSTiO2 was conducted via XRD,UV-vis,SEM,and photocurrent intensity.The experimental results show that Au-HSTiO2 exhibits prominently higher photocatalytic hydrogen production than TiO2 and HSTiO2.Enhanced photosynthetic hydrogen production ability of Au-HSTiO2 should be attributed to the presence of abundant surface active sites of HSTiO2,remarkably extending electronic holes in Au doping.This study provides a promising photosynthetic material for hydrogen production.

Bio-inspired Materials for Photocatalytic Hydrogen Production

After millions of years of evolution,species in nature have structures and complex elements that are difficult to synthesize artificially.Moreover,these fine structures and compositions are often beneficial to improve the photocatalytic performance.Therefore,various materials with special morphology,pore structure and element composition derived from biomass have emerged and are widely used.This mini review focuses on the preparation of bio-inspired materials and their current status in photocatalytic hydrogen production.Hopefully,this will bring new perspectives to researchers and make them learn more about the advantages of"learning from nature"and pay more attention to the green design of material structures.

Significantly enhanced photocatalytic hydrogen production performance of g-C_(3)N_(4)/CNTs/CdZnS with carbon nanotubes as the electron mediators

The electron mediator can effectively improve the performance of the direct Z-scheme heterojunction photocatalysts. However, it is still a great challenge to select cheap and efficient electron mediators and to design them into the Z-scheme photocatalytic system. In the present paper, the g-C_(3)N_(4)/CNTs/CdZnS Z-scheme photocatalyst was prepared using carbon nanotubes(CNTs) as the electron mediators, and its photocatalytic hydrogen production performance was studied. Compared with single-phase g-C_(3)N_(4),CdZnS and biphasic g-C_(3)N_(4)/CdZnS photocatalysts, the photocatalytic hydrogen production performance of the prepared g-C_(3)N_(4)/CNTs/CdZnS has been significantly enhanced. Meanwhile, g-C_(3)N_(4)/CNTs/CdZnS possesses very good photocatalytic hydrogen production stability. The enhanced photocatalytic hydrogen production performance of g-C_(3)N_(4)/CNTs/CdZnS is attributed to the fact that CNTs, as an electron mediator,can accelerate the recombination of the photogenerated holes in the valence band of g-C_(3)N_(4) and the photogenerated electrons in the conduction band of CdZnS, which makes the g-C_(3)N_(4)/CNTs/CdZnS Zscheme photocatalyst be easier to escape the photogenerated electrons, increases the concentration of the photogenerated carriers and prolongs the lifetime of the photogenerated carriers. This work provides a theoretical basis for the further development and design of CNTs as the intermediate electron mediator of the Z-scheme heterojunction photocatalyst.

Photophysical,optical,and photocatalytic hydrogen production properties of layered-type BaNb_(2-x)Ta_(x)P_(2)O_(11)(x=0,0.5,1.0,1.5,and 2.0)compounds

Layered-type metal phosphates of BaNb_(2-x)Ta_(x)P_(2)O_(11)(x=0,0.5,1.0,1.5,and 2.0)were synthesized using a solid-state reaction method.The photophysical,optical,and photocatalytic hydrogen production properties of the resulting powders were investigated for the first time.Phase-pure and homogeneous powders with irregular morphologies were obtained at a calcination temperature of 1200℃.As the Ta content increased,the interlayer distance along the c-axis increased by up to 0.14%.Additionally,the optical bandgap values increased from 3.32 to 3.59 eV.The energy band positions were estimated from the Mott–Schottky measurements.BaNb_(2)P_(2)O_(11)(x=0)exhibited the lowest conduction band edge position(-0.14 V vs.the normal hydrogen electrode,NHE),which is located above the water reduction potential(0.0 V vs.NHE).In comparison,BaTa_(2)P_(2)O_(11)(x=2.0)exhibited the highest conduction band edge position(-0.29 V vs.NHE),comparable to that of TiO_(2).The photocatalytic activity for hydrogen produced from splitting water was measured under ultraviolet light irradiation.Notably,BaTa_(2)P_(2)O_(11)exhibited the highest activity(7.3μmol/h),which was 15 and 10 times larger than BaNb_(2)P_(2)O_(11)(0.5μmol/h)and nano-TiO_(2)(0.7μmol/h),respectively.The activity of BaTa_(2)P_(2)O_(11)increased to 24.4μmol/h after deposition of the NiO_(x)co-catalyst(1 wt.%),which remained stable during continuous operation(~35 h).

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.

A comparison study of alkali metal-doped g-C_3N_4 for visible-light photocatalytic hydrogen evolution

Photocatalytic hydrogen production based on semiconductor photocatalysts has been considered as one of the most promising strategies to resolve the global energy shortage.Graphitic carbon nitride(g‐C3N4)has been a star visible‐light photocatalyst in this field due to its various advantages.However,pristine g‐C3N4usually exhibits limited activity.Herein,to enhance the performance of g‐C3N4,alkali metal ion(Li+,Na+,or K+)‐doped g‐C3N4are prepared via facile high‐temperature treatment.The prepared samples are characterized and analyzed using the technique of XRD,ICP‐AES,SEM,UV‐vis DRS,BET,XPS,PL,TRPL,photoelectrochemical measurements,photocatalytic tests,etc.The resultant doped photocatalysts show enhanced visible‐light photocatalytic activities for hydrogen production,benefiting from the increased specific surface areas(which provide more active sites),decreased band gaps for extended visible‐light absorption,and improved electronic structures for efficient charge transfer.In particular,because of the optimal tuning of both microstructure and electronic structure,the Na‐doped g‐C3N4shows the most effective utilization of photogenerated electrons during the water reduction process.As a result,the highest photocatalytic performance is achieved over the Na‐doped g‐C3N4photocatalyst(18.7?mol/h),3.7times that of pristine g‐C3N4(5.0?mol/h).This work gives a systematic study for the understanding of doping effect of alkali metals in semiconductor photocatalysis.

Enhanced photocatalytic H_(2) production performance of CdS hollow spheres using C and Pt as bi-cocatalysts

Photocatalytic H2 production from water splitting is an effective method to solve energy crisis and environmental pollution simultaneously.Herein,carbon@CdS composite hollow spheres(C@CdS-HS)are fabricated via a facile hydrothermal method using porous carbon hollow spheres(C-HS)as the template.The C@CdS-HS shows an excellent photocatalytic H2-generation rate of 20.9 mmol h^(−1) g^(−1)(apparent quantum efficiency of 15.3%at 420 nm),with 1.0 wt%Pt as a cocatalyst under simulated sunlight irradiation;this rate is 69.7,13.9,and 3.9 times higher than that obtained with pure CdS hollow spheres(CdS-HS),C@CdS-HS,and CdS-HS/Pt,respectively.The enhanced photocatalytic H_(2)-evolution activity of C@CdS-HS/Pt is due to the synergistic effect of C and Pt as the bi-cocatalyst.The C-HS serves not only as an active site provider but also as an electron transporter and reservoir.Moreover,C-HS has a strong photothermal effect that is induced by near infrared light,which kinetically accelerates the H_(2)-production reaction.Additionally,the underlying charge transfer pathway and process from CdS to C−HS is revealed.This work highlights the potential application of C-HS-based nanocomposites in solar-to-chemical energy conversion.

Heterostructuring noble-metal-free 1T'phase MoS_(2) with g-C_(3)N_(4) hollow nanocages to improve the photocatalytic H2 evolution activity

In this work,we report the preparation of 1T'-MoS_(2)/g-C_(3)N_(4) nanocage(NC)heterostructure by loading 2D semi-metal noble-metal-free 1T'-MoS_(2) on the g-C_(3)N_(4) nanocages(NCs).DFT calculation and experimental data have shown that the 1T'-MoS_(2)/g-C_(3)N_(4) NC heterostructure has a stronger light absorption capacity and larger specific surface area than pure g-C_(3)N_(4) NCs and g-C_(3)N_(4) nanosheets(NSs),and the presence of the co-catalysts 1T'-MoS_(2) can effectively inhibit the photoinduced carrier recombination.As a result,the 1T'-MoS_(2)/g-C_(3)N_(4) NC heterostructure with an optimum 1T'-MoS_(2) loading of 9 wt%displays a hydrogen evolution rate of 1949 mmol h^(-1) g^(-1),162.4,1.2,1.5,1.6 and 1.2 times than pure g-C_(3)N_(4) NCs(12 mmol h^(-1) g^(-1)),Pt/g-C_(3)N_(4) NCs(1615 mmol h^(-1) g^(-1))and Pt/g-C_(3)N_(4) nanosheets(NSs,1297 mmol h^(-1) g^(-1)),1T'-MoS_(2)/g-C_(3)N_(4) nanosheets(1216 mmol h^(-1) g^(-1))and 2H-MoS_(2)/g-C_(3)N_(4) nanocages(1573 mmol h^(-1) g^(-1)),respectively,and exhibits excellent cycle stability.Therefore,1T'-MoS_(2)/g-C_(3)N_(4) NC heterostructure is a suitable photocatalyst for green H_(2) production.