Construction Of Biomass Carbon Quantum Dots Modified The Bismuth-based Photocatalyst And Study On The Photodegradation Performances Of Typical Pharmaceutical In Water

Due to the advantages of low-cost,easy operation,photocatalytic technology can better utilize and convert green and sustainable solar energy,which has attracted extensive attention in pollutant degradation in wastewater,air pollution control,hydrogen fuel production,and carbon dioxide reduction.The development of environmental-friendly and sustainable green photocatalysts for the treatment of pharmaceuticals and personal care products（PPCPs）in the water environment using clean solar energy is an urgent and significant challenge in the field of water treatment.Bismuth-based photocatalysts are considered promising photocatalysts due to their low cost,low toxicity,good stability,and optical properties.However,the monomeric bismuth-based photocatalysts are easy to agglomerate and the ability of visible light response is poor,which is greatly limited in practical applications.Modification of bismuth-based photocatalysts such as doping,interfacial regulation,and construction of heterojunctions can effectively improve their photocatalytic performance.Biomass-derived carbon quantum dots（CQDs）are more environmentally friendly than those prepared using chemical precursors.And CQDs could be a promising electron transfer intermediary candidate because of their low toxicity,high chemical stability,photo-generated electron transfer,and excellent up-conversion luminescence abilities,which has attracted growing attention.In this study,four kinds of bismuth-based composite photocatalysts with excellent photocatalytic activity were prepared in view of the shortcomings of the bismuth-based photocatalysts.The typical analgesic drug carbamazepine and the widely used sulfonamide antibiotics were used as target pollutants to study the photocatalytic activities and practical application potential of the prepared photocatalysts,which could provide a new strategy for the preparation of green photocatalysts for the treatment of typical pharmaceuticals in water.The main research contents and conclusions of this study are as follows:（1）Biochar（BC）and biomass carbon quantum dots（CQDs）were used to modify Mg In₂S₄/Bi OCl（MB）heterojunction photocatalyst with a Z-scheme structure,which improved the photocatalytic degradation performance for carbamazepine（CBZ）in the aqueous solution.Both BC and CQDs could form an electron transfer interface with MB heterojunction,resulting in the photodegradation rate of Mg In₂S₄/Bi OCl/CQDs（MBC,96.43%）and Mg In₂S₄/Bi OCl/BC（MBB,88.09%）to CBZ within 120 min visible-light irradiation were significantly higher than that of MB（65.84%）.Moreover,photoelectrochemical and photoluminescence tests verified that CQDs could act as a bridge for storing and transferring electrons in the entire Z-scheme system.Thence,compared with MBB,MBC could produce more·OH and·O₂^-under the visible light,which was indicated by the results of radical quenching experiments and electron paramagnetic resonance.Interestingly,under the natural sunlight,the photocatalytic performance of MBC to CBZ was even better than under laboratory conditions.In addition,the TOC removal efficiencies of MBB and MBC could reach 85.09%and93.79%respectively.Finally,compared with other composites,MBB and MBC showed higher photocatalytic performance and lower energy consumption,which would provide a green strategy for biochar materials in the photocatalytic treatment of typical pharmaceutical in water.（2）N-doped biomass carbon quantum dots（N-CQDs）decorated p-n heterojunction photocatalyst Bi O_2-x/Bi OCl was prepared using a facile two-step strategy.By the results of SEM and TEM,the Bi OCl nanosheets were uniformly distributed on the rod-shaped Bi O_2-x by HCl etching,and the deposition of N-CQDs on the composite photocatalyst could be observed.The introduction of N-CQDs into Bi O_2-x/Bi OCl would effectively inhibit the recombination of photogenerated charge carriers because N-CQDs could gather electrons.Furthermore,the results of XPS analysis indicated that the internal electric field generated by N-CQDs/Bi O_2-x/Bi OCl（BBN）could induce the charge transfer and form a stable p-n heterojunction structure in the system.The photodegradation efficiency of BBN to sulfamethoxazole（SMX）could reach 96.48%within 30 min visible light irradiation,and the TOC removal efficiency which was 89.40%.Also,the photodegradation rate of other six sulfonamide antibiotics could also reach more than 95%.The presence of common anions(Cl-,NO₃^-,SO₄^2-)and natural organic matter（NOM,HA）in water promoted or inhibited the photocatalytic degradation of SMX to a certain extent.As a consequence,this work would provide a design of high-quality photocatalysts and a green-promising strategy for bismuth-based photocatalysts in the water treatment of typical pharmaceutical.（3）Bi~0-modified Bi OCl/N,S-CQDs was synthesized by a simple chemical reduction method.By characterizing the morphology of the composite photocatalyst,it was easy to find that there was a flower-like structure of N,S-CQDs/Bi OCl after Bi~0deposition,which was beneficial to improve the visible light absorption and multilayer refraction of the composite photocatalyst under visible-light irradation.Compared with Bi OCl,Bi~0/Bi OCl/N,S-CQDs exhibited excellent photodegradation performance for target pollutant sulfathiazole（STZ）under visible light irradiation.The enhanced photocatalytic activity was mainly because the introduction of N,S-CQDs and Bi~0could improve the light absorption and rapid separation of photogenerated carriers.The quenching experiments showed that·O₂^-and h⁺were the main active species for the photodegradation of STZ.In addition,five-cycle photodegradation experiments demonstrated that the composite photocatalyst had great repeatability and stability.Thence,it could provide a new strategy for non-precious metal in-situ plasma-modified bismuth-based photocatalysts to degradation typical pharmaceutical residues in polluted water.