Construction Of LaVO₄ Composites Materials And Their Photocatalytic Activities In Degradation For Pollutants

With the rapid development of industry and the rapid growth of population,the accumulation of emerging environmental organic pollutants such as pesticides,phenols and antibiotics has increased speedily,then poses severe threats to human health and aquatic ecosystems.Among methods to solve serious water pollution,photocatalysis technology stands out by virtue of its advantages of direct utilization of solar energy,no secondary pollution and so on,and has attracted extensive attention from researchers.However,it is still a great challenge to prepare new photocatalysts with wide absorption range,high catalytic activity and strong chemical stability.In addition,it is necessary to systematically analyze the degradation pathways,degradation products and toxicity of pollutants,but only a few studies have been reported so far.Lanthanum vanadate?LaVO₄?has great potential in photocatalysis field because of its high chemical stability,good optical properties and certain surface catalytic properties.Previously,research on LaVO₄ mainly focused on its photoluminescence ability,while its photocatalytic performance was rarely reported,which mainly results from its low light absorption strength,slow migration of charge carriers and rapid recombination rate of photo-generated electron and hole pairs.In this dissertation,the separation efficiency of photo-generated electron and hole pairs has improved by modified with carbon materials.To essential improve the photocatalytic degradation activity of LaVO₄,the synthesis method of pure LaVO₄ has optimized.On this basis,the red carbon nitride?C₃N₄?has introduced to regulate the migration path of electron and hole pairs so that improve the photocatalytic degradation performance.The main research contents are summarized as follows:1.Carbon tube?CNT?was used to modify LaVO₄ to construct CNT/LaVO₄nanostructures by one-step hydrothermal method.The phase structures,chemical compositions,morphologies,and optical properties of the prepared samples were investigated via various characterization techniques.The optimized CNT/LaVO₄nanostructures exhibited efficient photodegradation activity with remarkable stability.The 0.1%CNT/LaVO₄ showed the highest tetracycline degradation rate,which is 2times that of pure LaVO₄.This design successfully expedites the separation and transfer of photogenerated charge carriers.The electron spin resonance?ESR?spin-trap technique,free radical trapping experiments and mass spectrometry analysis?MS?were used to identify the active species,intermediate product,photodegradation pathway and reaction mechanism during the photocatalytic process.The antibacterial results showed that the degrading products have lower toxicity.2.GO/LaVO₄ composite materials were fabricated via a one-step hydrothermal method,which presented enhanced photocatalytic degradation efficiency for tetracycline?TC?and naproxen?NPX?under visible light irradiation.It was found that 0.01%GO/LaVO₄ presented the highest degradation rate with good stability,which is 3.46-times?for TC?and 2.29-times?for NPX?compared with that pure LaVO₄.In particular,the intermediates of TC produced during the photodegradation reaction and the corresponding possible degradation pathway were analyzed in depth by mass spectrometry?MS?.Through the design of toxicology experiments,the toxicity of the TC solution was eliminated after the photocatalytic treatment.These results indicated that the modification of GO could efficiently improve the optical absorption property and accelerate the separation and migration of photo-generated charge carriers,thus enhancing the photocatalytic activity.3.LaVO₄ nanorods were obtained by optimizing the synthesis condition to improve its photocatalytic performance.On this basis,red carbon nitride?C₃N₄?was introduced to form Z-scheme C₃N₄/LaVO₄?CNL?composite photocatalytic system.The photocatalytic degradation experiments on TC and NPS showed that 5%CNL material presented the best photocatalytic performance,which was 3 times?for TC?and 2.5 times?for NPX?higher than pure LaVO₄,respectively.The cyclic experiments show that CNL composites have good chemical stability.The analysis of band structure,electron spin resonance?ESR?spin-trap technique and free radical trapping experiments showed that,under visible light irradiation,the h⁺at valence band?VB?of LaVO₄ recombined with the e^-at conduction band?CB?of C₃N₄,thus the electron-hole recombination rate was reduced.The h⁺at VB of C₃N₄ and e^-at CB of LaVO₄ participated in the final photocatalytic process to achieve high redox ability and improve the use of sunlight,eventually realize the rapid degradation of pollutants.