Construction and Characteristic of Red Phosphorus-Based Photocatalysts for Synergistic Removal of Cr(Ⅵ) and Organic Pollutants

Author:Bai Xue

Supervisor:fan jun

Database:Doctor

Degree Year:2019

Download:147

Pages:133

Size:12558K

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With the continuous development of nowadays society,the energy and environment problems are two major global issues,which have increasingly prominent and become the main obstacles to economic and social development.Photocatalytic technology,as a green and sustainable chemical technology,can realize the conversion from solar energy to chemical energy,which is expected to be one of the best ways to solve the problems of environmental deterioration and energy crisis.For a long time,the research focused mainly on the following points:broaden the light absorption edge of photocatalyst to improve absorption efficiency,improving the photogenerated charge separation and transfer efficiency to inhibit carriers recombination,and reducing the overpotential of surface reaction to enhance the photocatalytic ability.To this end,choice and development of appropriate photocatalysts focus on above needs is a key step to make tech advancements.Due to the unique physical and chemical properties of 2D photocatalyst,suitable band structure of red phosphorus(RP)semiconductor and its excellent photocatalytic performance in related reports,the rational development of RP based 2D photocatalyst has a wide prospect of application.In this paper,RP and common 2D materials(MoS2,GO and TiO2 nanosheets)are served as primary catalysts,morphology control and 2D heterojunction construction are used to improve the photocatalytic efficiency and stability of RP.The core content of the thesis is to explore the reason of superior performance of the synthesized photocatalytic system in light absorption,separation and transformation of photogenerated charge carriers,and surface chemical reaction process.Finally,photocatalytic simultaneously remove of Cr(VI)and various organic pollutants in water are investigated,which shows promising application to treatment the reality wastewater and expands the idea for solving practical environmental problems.The main contents of this dissertation are summarized as follow:(1)Two mehods of Physical ultrasonic stripping and chemical hydrothermal were chosen to modify the original RP.By comparing the characterization results of the microscopic morphology,chemical constitution,optical response ability and photoelectric properties of the samples,it was confirmed that the RP modified by chemical hydrothermal(n-RP)with a nano-layered structure presents better adsorption ability and higher photogenerated charge separation and transfer efficiency,resulting in a better photocatalytic performance.Furthermore,n-RP maintains an efficient and stable photocatalytic activity even after four cycles.In conclusion the nano-structure modification engineering of RP semiconductor is an effective strategy to improve their photocatalytic performances.The n-RP was used as the reactant for the subsequent studies.(2)A novel 2D MoS2/RP heterojunction photocatalyst with intimate interfacial contact through chemical bonds of S=P was successfully fabricated through a facile in situ hydrothermal method for the first time.The photocatalytic activity of the nano-composite was evaluated by the removal of the Cr(VI)-RhB coexistence system under visible light irradiation,to 72.7%for Cr(VI)and 97.5%for RhB simultaneously in 80 min.And the reduction of Cr(VI)into Cr(III)/(0)happened over MoS2/RP photocatalyst under visible light illumination was analysed via the XPS.The photoelectrochemical analyses revealed that the MoS2/RP composites show an outstanding charge separation ability compared to the pristine RP,resulting in the enhanced photocatalytic activity,which further confirmed that the in situ hydrothermal method gave rise to an excellent interfacial contact between the layered RP and MoS2.In particular,it can be considered as an efficient and meaningful2D heterojunction building method,moreover,provides guidance to further design of photocatalyst toward various applications.(3)The flat carbon of GO was served as a scaffold to anchor MoS2,and obtained MoS2/rGO hybrid was fabricated to stabilize and improve the dispersibility of RP.The above obtained appropriate nanostructure of RP-MoS2/rGO with high-performance photocatalyst,through a facile two-step hydrothermal method,present a good adsorption ability,which can assist in promoting selectivity and efficiency of the catalytic process.Even without a noble-metal cocatalyst,the introduction of MoS2/rGO hybrid made RP exhibit excellent photocatalytic performance,including photoreduction of Cr(VI)and photooxidation of different organic pollutants,owing to the increased number of excited electrons/holes and enhanced separation efficiency of charge carriers.Importantly,the synergy of photocatalytic reduction and oxidation,as well as photocatalysis and adsorption played an important role in enhancing photocatalytic activity and reaching a high efficiency.Besides,the chemical structure of the RP-MoS2/rGO with P-S and P-O bands ensure the stability of the nanocomposite materials.Overall,the photocatalytic elimination of the Cr(VI)-Organic molecule coexistence system in this work shows promising application to treatment the reality wastewater.(4)Titanium oxide(TiO2)nanosheets with red phosphorus(RP)by simply hydrothermal treatment can fabricate P-doped anatase TiO2 nanosheets with variation in surface species viz.Ti4+,O2-,Ti3+,oxygen vacancies(Vo)and P5+.The defect and impurity levels induced by moderate doping could facilitate the formation of charge trap centers or avoid the formation of charge recombination centers and result in significantly improved photocatalytic activity.Moreover,the enhanced optical absorbance and transfer performance of photo-generated carriers were studied using UV-Vis spectroscopy,photoelectric spectrometry and TR-PL.Importantly,the formation of Ti-O-P bands may accelerated transmission of electrons,giving rise to the effective separation of photo-generated carriers.To the best of our knowledge,the Cr(VI)and RhB removal rate obtained by this hybrid show comparatively competitive among other reports so far.It is believed that this work provide a promising approach for building a novel pathway for electron transport and more photocatalytic reaction centers on photocatalysts.