Preparation Of Single Atom Pt₁/TiO₂ By Freezing Photoreduction For High-efficiency Photocatalytic Hydrogen Production

Single-atom catalysts become the ideal axis to connect homogeneous catalysts and heterogeneous catalysts.It has the advantages of stable heterogeneous catalysts,100%active center atom utilization,low active center atomic ratio,and uniform active center structure.The currently prepared monoatomic methods are:wet chemistry,mass separation-soft landing method,diffusion method,monoatomic layer deposition,solid phase melting,wet chemical synthesis method,defect engineering strategy,space constraint strategy,coordinated design strategy,sacrifice Template method,electrochemical corrosion method,etc.However,monoatomic catalysts have problems such as high surface energy and easy agglomeration,incomplete preparation methods of monoatomic dispersive catalysts,and in-depth understanding of the reaction mechanism.Based on this,by using ethylene glycol-protected TiO₂ as a carrier and adopting the freeze-light reduction method,a high-price single-site platinum catalyst is prepared.First,TiO₂ and H₂PtCl₆ are mixed uniformly.PtCl₆^2-binding,under freezing conditions,can prevent the aggregation of Pt atoms and successfully stabilize the single atoms.The free radicals on the surface of TiO₂ are excited by ultraviolet light to generate free radicals,which helps the removal of chloride ions,through Pt-O bonds.Platinum was fixed on the surface of TiO2 to prepare a high-priced single-site platinum catalyst.Work in three areas:（1）Preliminary study on preparation of monoatomic Pt/TiO₂ for photocatalytic hydrogen production by freezing photoreductionFirst,the effect of fluoride on P25 was studied,and it was found that platinum did not change the crystal structure of P25,but the presence of glucose reduced the specific impurity of P25.Carbon dioxide modified P25 has a positive surface doping enhancement,which may be due to the calcium fluoride and positively charged in the plasma,which may increase the electrostatic adsorption of the precursor(PtCl₆^2-)to achieve the loading goal;different catalysts we studied（P25-n5,P25-I5,PE-n5,PE-I5）photocatalytic hydrogen production activity,in which the phosphoric acid modified P25,the hydrogen production activity of the catalyst prepared by freeze-light reduction（PE-I5:22.81 mmol/g/h;Pt w%:0.14%）catalyst（PE-n5:15.49 mmol/g/h;Pt w%:0.26%）.（2）Preparation of monoatomic Pt/TiO₂ for photocatalytic hydrogen production by freeze photoreduction under different conditionsThe catalyst was prepared by optimizing the freeze reduction of the grade conditions,including the following aspects:drying time of modified P25（PE）,ice thickness,different freezing methods,NaOH etching at different times,different volume particle sizes,P25 and different alcohol-modified P25.Different freezing light reduction time,UV pretreatment and different TiO₂.Optimal conditions were selected.The catalyst P（Na）E-UV-I5（Pt₁/TiO₂）（30.30 mmol/g/h）produced by freeze photoreduction had higher hydrogen production activity than the catalyst P25-n5（14.87 mmol/g/h）,we found by ICP measurement that the Pt content（ICP:Pt,0.12%）of the catalyst P（Na）E-UV-I5（Pt₁/TiO₂）prepared by freezing photoreduction was converted to P25-n5（ICP:Pt,0.22%）,which further proves that the photocatalytic hydrogen production performance of Pt-supported catalysts prepared by freezing photoreduction is higher than that of Pt-supported catalysts prepared by ordinary photoreduction.（3）Exploration of mechanism and activity expansion of monoatomic Pt₁/TiO₂prepared by freezing photoreductionUnder the same loading of Pt,the photocatalytic hydrogen production activity of the catalyst prepared by freezing photoreduction（Pt₁/TiO₂:30.30 mmol/g/h）is higher than the catalyst prepared by ordinary photoreduction（Pt NP/TiO₂:5.87 mmol/g/h）,which is about 5.2 times;we also further proved that the Pt particles on the catalyst surface prepared by freeze-light reduction are an unsaturated coordination state through TEM and XPS;through spherical aberration electron microscopy,we found that freeze-light reduction The prepared catalyst has Pt single atom on the surface.The catalyst prepared by freeze photoreduction is not only higher than the catalyst prepared by ordinary photoreduction in photocatalytic hydrogen production,but also has certain research significance in CO₂ reduction,toluene oxidation and hydrosilylation,and further research is needed.