The Preparation Of Photocatalysts Based On G-C₃N₄ And Discussion The Mechanism Of Photocatalytic Degradation Of Organic Pollutants

Every year,a large number of organic pollutants are discharged into the environment,e.g.wastewater containing chemical dyes in industrial production,antibiotic-containing excreta from animal husbandry and medical life.Chemical dyes are relatively common organic pollutants,e.g.RhB.Azo dyes RhB is widely existed in the wastewater from textiles,cosmetics,and printing,which has been investigated a lot due to its toxicity and non-biodegradation.Besides,antibiotics have been a major concern in recent years.Among the used antibiotics,tetracyclines and fluoroquinolones were the most consumed.Tetracycline?TC?and ciprofloxacin?CIP?as representative tetracyclines and fluoroquinolones antibiotics respectively have been detected excessively accumulation in the aquatic environment.Studies on the effluents of hospital and pharmaceutical manufacturing wastewaters showed that the CIP and TC upped to 31 mg/L and 100-500 mg/L,respectively.The antibiotics in the aquatic environment raised increasing concerns about potential adverse effects on human health and aquatic ecosystems.Exposure to antibiotics may lead to metabolic and immune diseases mediated by gut microbiota,e.g.diabetes,inflammatory bowel disease,etc.Antibiotics cannot be effectively degraded by traditional sewage treatment techniques due to the inhibition of the proliferation of bacterial.It is critical to effectively remove them in environment.To date,various methods have been explored to removal organic pollutants,including adsorption,biodegradation,photocatalysis,ultrasonic.Among these,photocatalysis has been considered as an effective method for wastewater treatment due to its superb oxidation ability to degradation organic pollutants and mineralize most toxic compounds completely.g-C₃N₄ as a metal free polymer semiconductor photocatalyst with band gap energy of 2.7 eV attracting great attention in the fields of photocatalysis due to the advantages of stable thermochemical properties,simple preparation method,easily access to raw materials and certain response to visible light.In this article,the composites based on g-C₃N₄were prepared and the photocatalytic mechanism towards degradation of organic pollutants was studied.Two composites based on g-C₃N₄ have been synthesized by construction of Z scheme heterojunction,morphology control,element doping and loading cocatalysts.And then the photocatalytic performance of the prepared g-C₃N₄based composites was tested by degradation of organic pollutants as target pollutants under different light irradiation.Based on the experimental and characterization results,proper mechanism of photocatalytic degradation of organic pollutants has been proposed.The detail experiment results and research contents of this study were showed as follows:?1?The Z scheme g-C₃N₄ quantum dots/ultrathin Bi₂WO₆ nanosheets composites?CNQDs/BWO?were synthesized by reflux,the photocatalytic degradation experiments showed that the CNQDs/BWO composites have good photocatalytic activity for the degradation of organic pollutants.The 5%CNQDs/BWO exhibited the best photocatalytic performance.It could degrade 87%and 92.51%TC and RhB within 60 min under visible light,respectively.And its degradation efficiency to TC was² times than pure BWO in 60 min under NIR light.The upconversion behavior of CNQDs by convert near-infrared light to visible light contribute to the enhanced utilized of light of composites,thereby the composites showed photocatalytic performance under NIR light irradiation.The catalytic mechanism in visible light and NIR light is considered to be the same,which was deduced from their similar degradation trend.The enhanced photocatalytic activity of CNQDs/BWO under wide spectrum light irradiation can be ascribed to a Z-scheme charge transfer mechanism,which can accelerate the separation and transfer of photo-generated charges to retain the strong redox ability.In a word,the introduction of CNQDs to construct the CNQDs/BWO composites could significantly improve the photocatalytic performance under visible light and NIR light,and then enhance its degradation efficiency against organic pollutants.?2?The P doped hollow tubular g-C₃N₄/WC composites?P-TCN/WC?were synthesized by calcination process,the photocatalytic degradation experiments showed that the P-TCN/WC composites have good photocatalytic activity for the degradation of antibiotics.The 8%P-TCN/WC exhibited the best photocatalytic performance.It could degrade 93.76%and 76.21%TC and CIP within 120 min under visible light,respectively.The enhanced photocatalytic activity of P-TCN/WC can be ascribed to the expanded light absorption and decreased the recombination of charge carriers two aspects.On the one hand,P doping expanded the light absorption edges and hollow tubular morphology boosted the utilization of light,further,the light absorption of P-TCN/WC was expanded over the whole visible light region due to WC loading.In a word,more holes and electrons would be excited in the P-TCN/WC.On the other hand,the platinum like noble metal cocatalytic properties of WC and P doping made the recombination of carriers decreased obviously no matter bulk or space.Namely,the excited holes and electrons in the P-TCN/WC would be used for the degradation of antibiotics.