Preparation And Application Of Attapulgite Composites In Photocatalytic Conversion Of Cellulose

With the continuous increase of global energy consumption,renewable biomass energy is expected to alleviate the energy crisis.If biomass energy is directly converted into hydrocarbon fuel,it can not only solve environmental problems,but also develop new energy.Photocatalysis can selectively convert agricultural and forestry wastes directly into high value-added products.Compared with traditional catalysis,it has the advantages of low energy consumption and mild reaction conditions.Generally,photocatalysts can only utilize the ultraviolet wavelength of sunlight,the photogenerated electron holes are easy to recombine,the activity and selectivity of direct conversion of biomass are poor,and the catalyst cost is high,which limits its practical application in industry.In this paper,using palygorsktie clay（Pal）as matrix,Cu₂O QDs/Cu-Pal,Cu₂（PO₄）（OH）/P-Pal,and CuFe₂O₄/Fe-Pal nanocomposites were synthesized by microwave hydrothermal method.The application of photocatalytic conversion of cellulose was evaluated,and the mechanism of photocatalytic reforming was discussed.The main work of this paper is as follows:1.The hydrochloric acid-modified attapulgite lattice was reconstructed by copper ion ammonia distillation to prepare Cu₂O QDs/Cu-Pal nanocomposites for photocatalytic cellulose reformation to produce lactic acid.The results show that Cu-Pal has visible spectral response,and Cu₂O QDs can broaden the photo-response range of the material to the near-infrared.A type-II heterojunction is formed between Cu₂O QDs and Cu-Pal,which reduced the electron-hole（e^--h⁺）recombination rate and maintained a strong redox ability.The superoxide radical generated at the reducing end can oxidize theβ-1,4-glycosidic bond of the cellulose chain to obtain glucose,which was converted into lactic acid under the combined action of Lewis acid and surface holes of Cu₂O QDs.When the loading of Cu₂O QDs was 10 wt%,under the irradiation of 300W xenon lamp,the yield of lactic acid was the highest,which was 38.5%,and the conversion rate of cellulose was 83%.2.Pal was modified with phosphoric acid,and Cu₂（PO₄）（OH）/P-Pal photocatalytic composites were prepared by microwave hydrothermal method.In situ growth of Cu₂（PO₄）（OH）nanosheets with photothermal effect on the surface of P-Pal exhibits plasmonic resonance effect and good broad-spectrum absorption effect.Cu₂（PO₄）（OH）plasmon resonance can also generate hot electrons for the generation of superoxide radicals,while providing local thermal effects to improve the efficiency of photocatalytic reforming of cellulose.The abundant acidic sites on the surface of Cu₂（PO₄）（OH）and its metal coordination unsaturated sites were beneficial to capture oxygen atoms in glucose and dehydrated and isomerized glucose to form 5-hydroxymethylfurfural（5-HMF）.It was found that under simulated sunlight irradiation,when the mass fraction of P-Pal was 20 wt%,the composite effect was the best.The yield of 5-HMF,fructose,2,5-furandicarbaldehyde（DFF）were 72%,19%and 9%,respectively.The photothermal conversion of cellulose into 5-HMF was realized,which provided a new idea for the conversion and utilization of cellulose.3.CuFe₂O₄/Fe-Pal photocatalytic composites were prepared by microwave hydrothermal method and applied to photocatalytic cellulose reformation to DFF and coupled photocatalytic nitrogen fixation.The results showed that Pal provided an intermediate energy level after lattice reconstruction of Fe ions,reduced the Pal band gap,and cooperated with Fe sites in CuFe₂O₄ to provide nitrogen adsorption activation sites,and the Cusites promote the isomerization reaction.Under simulated sunlight,when the mass ratio of CuFe₂O₄was 12 wt%,the nitrogen fixation reduction performance of the composite was the best,the generation rate of NH⁴⁺was about 390μmol·g^-1_cat·h^-1,and the conversion rate DFF yield was 80%.The CuFe₂O₄/Fe-Pal photogenerated e^--h⁺follows the Type-II heterojunction mechanism,which can effectively separate photogenerated electrons and holes,thereby improving the utilization of sunlight and the efficiency of photocatalytic redox reactions.