Reasonable Design And Enhanced Photocatalytic Performance Of CdLa₂S₄-Based Composites

The energy crisis and environmental pollution are two major challenges facing human society since the 21st century.The non-renewable fossil energy and the large amount of greenhouse gas emissions after combustion further aggravate environmental pollution.Therefore,it is urgent to seek a clean energy source to gradually replace modern industry’s reliance on fossil fuels.Semiconductor based photocatalytic technology can be used for water decomposition,carbon dioxide reduction,pollutant degradation,nitrogen fixation,and sterilization,and is considered an ideal way to solve energy and environmental problems.Photocatalytic technology has a history of several decades,and many semiconductors have been developed and used as photocatalysts for some photocatalytic reactions.Among many semiconductor materials,transition metal sulfides are abundant,inexpensive,and have good visible light response ability,and are widely used in the field of photocatalysis.However,metal sulfides are prone to photoetching,and their active sites lead to poor photocatalytic activity and stability,which limits the further application of this material.As a visible light responsive semiconductor material,ternary transition metal sulfide CdLa₂S₄ also has the problems of insufficient active sites and poor photocatalytic stability.In order to solve these problems,doping semiconductors or supporting cocatalysts can provide rich active sites for reaction and improve the photocatalytic activity of semiconductor materials.Choosing a semiconductor with band matching to composite with metal sulfides to construct a heterojunction can optimize the transfer path of photo generated carriers and avoid the reaction of photo generated holes on the surface of sulfides,which can improve the problem of sulfide corrosion.Based on the above considerations,this article has carried out the following work,specifically as follows:（1）CdLa₂S₄ nanoparticles were synthesized by solvothermal method.In order to further enhance their photocatalytic activity,the synthesized CdLa₂S₄ nanoparticles were subjected to a secondary solvothermal reaction with nickel acetylacetonate in DMF solvent.By adjusting the reaction time,a series of Ni doped and Ni nanoparticles loaded CdLa₂S₄ nanoparticles were obtained Ni-CdLa₂S₄@Ni Composite photocatalyst.After conducting photocatalytic hydrogen evolution tests under visible light,it was found that,The Ni-CdLa₂S₄@Ni-12 composite photocatalyst exhibits the optimal photocatalytic hydrogen evolution rate,reaching 6.95 mmol g^-1 h^-1,which is approximately 116 times that of pure CdLa₂S₄.After UV-vis-IR DRS testing of the synthesized catalyst,it was found that the absorption band edge of the doped composite material underwent a red shift,and the absorbance and light absorption range were significantly improved.HR-TEM test results show that doping can produce dislocation structure in CdLa₂S₄nanoparticles,which can form rich reaction active site in the catalyst.At the same time,XRD and XPS confirmed the existence of Ni nanoparticles.After analyzing the reaction mechanism,it was found that doping would narrow the band gap of the catalyst,and the existence of Ni nanoparticles could couple with CdLa₂S₄to form Schottky heterojunction.The existence of heterojunction realized the effective separation of photogenerated carriers.Ni nanoparticles could also be used as a co catalyst,which greatly improved the photocatalytic activity of metal sulfides.Therefore,this work provides new ideas for designing efficient metal sulfide based photocatalysts.（2）The aboved work found that doping and construction of heterojunction can significantly improve the activity of the catalyst,and the LSPR effect of metal nanoparticles can produce excellent local thermal effect to accelerate the transport of carriers.Considering the advantages of two-dimensional layered black phosphorus nanosheets such as high conductivity and adjustable band gap,coupling them with CdLa₂S₄ nanoparticles through solvothermal method can fully expand the light absorption range of the catalyst.Introducing nickel salts in the solvothermal reaction process not only allows for in-situ generation of Ni₂P co-catalysts on the surface of black phosphorus nanosheets,but also enhances the stability of black phosphorus nanosheets..At the same time,the reducing solvent DMF can reduce Ni²⁺to Ni nanoparticles.By adjusting the amount of nickel salt added during the reaction process,a series of CdLa₂S₄/BP@Ni₂P/Ni composite photocatalyst were obtained.The optimal hydrogen evolution rate of CdLa₂S₄/BP@Ni₂P/Ni-80 composite photocatalyst is about 10.80 mmol g^-1 h^-1,the photocatalytic activity and stability were significantly improved compared to the first work.Through UV-vis-IR DRS testing,it was confirmed that the catalyst improved the light absorption range and absorption ability.The infrared thermal imaging test results showed that the introduction of black phosphorus can produce excellent thermal effects.The photoelectrochemical test of the catalyst shows that Ni₂P and Ni nanoparticles can be used as co-catalysts to accelerate the migration of photogenerated electrons and inhibit the recombination of photogenerated electrons and holes.After analyzing the mechanism of photocatalytic reaction,it can be concluded that the improvement of photocatalytic efficiency comes from the combined effect of various favorable factors such as heterojunctions,co catalysts,and photothermal effects.This work provides unique thinking for designing efficient non precious metal photocatalysts and photothermal assisted photocatalysts.（3）Using Co₃O₄ as the precursor,a simple two-step solvothermal method was used to obtain CdLa₂S₄@La（OH）₃@Co₃S₄Composite photocatalysts,in which Co₃S₄is obtained through in-situ sulfurization of Co₃O₄,have a narrow band gap and can absorb most of the visible light,even near-infrared light.The UV-vis-IR DRS test showed a significant improvement in the absorption performance of the composite material in the near-infrared region.Infrared thermal imaging testing shows that the composite material has excellent photothermal conversion characteristics.After conducting photocatalytic hydrogen evolution reaction tests on the ternary photocatalyst and analyzing its photocatalytic mechanism,it was found that the reaction mechanism of the catalyst under visible light and simulated sunlight irradiation was Type-II and Z-scheme heterojunctions,respectively.The successful construction of the Z-scheme heterojunction enabled the catalyst to retain the strongest conduction and valence bands of redox ability,demonstrating excellent photocatalytic performance,which can not only be used for photocatalytic hydrogen production,It also exhibits excellent performance in photocatalytic carbon dioxide reduction and photocatalytic degradation,with a photocatalytic hydrogen production rate of 26.4 mmol g^-1 h^-1 under simulated sunlight,and the reduction rate for carbon dioxide to CH₄ and CO is 19.5μmol g^-1 h^-1 and 2.5μmol g^-1 h^-1,respectively.The degradation rate of tetracycline also reached 88%.Therefore,this composite material has multiple functions to improve energy and environmental issues,providing a new perspective for the synthesis of multifunctional photocatalysts with broad spectrum light absorption.