Synergistic Mechanism Of Adsorption And Photodegradation For Dyes Removal By Biochar/TiO₂ Composites

With the rapid development of urbanization and industrialization,water pollution in China has become increasingly severe,as the discharge of large amounts of wastewater from production processes has caused significant environmental damage.Azo dyes are considered the most widely consumed synthetic dyes in industrial activities,which have high chemical inertness and complex composition in wastewater,making them more difficult to be decolorized using physical and chemical methods compared to natural dyes.Azo dyes and their degradation products are biological toxicity,and their large-scale discharge will also cause serious harm to the environment.Among various dye wastewater treatment technologies,the synergistic combination of adsorption and photocatalysis is an advanced approach for wastewater treatment,characterized by its high-efficiency,energy-saving,environmentally friendly and low-cost advantages.This approach become a research hotspot in the field of environmental remediation.The photocatalytic activity of the photocatalysts primarily depends on the bandgap,catalytic active site,and generation of electron-hole pairs.Biochar as an adsorbent has abundant surface functional groups and a large specific surface area,which can be used to enhance the contact area of photocatalyst TiO₂ and pollutants,thus improving degradation efficiency.In addition,carbon doping can alter the bandgap width of TiO₂,and promote the generation of electron-hole pairs,which improve the photocatalytic activity.Moreover,the photocatalytic degradation can degrade adsorbed organic pollutants,allowing biochar to regain its adsorption capacity,achieving the effect of recycling.In this study,biochar was prepared from agricultural and forestry waste biomass,and then combined with self-made TiO₂ to investigate the mechanism of―adsorption+photocatalysis‖synergistic effect for azo dye removal.The modified sycamore biochar has abundant pore structure,which is conducive to the loading of TiO₂ nanoparticles.In this study,highly active TiO₂ nanoparticles were prepared by the sol-hydrothermal method through the regulation of solvent ratio,temperature,atmosphere and precursor treatment method.Powdered biochar with high porosity and strong adsorption capacity was prepared by modifying sycamore leaves with potassium carbonate,and powdered biochar/TiO₂ composites were obtained by compounding biochar and TiO₂ in different ratios using a two-step pyrolysis-hydrothermal method.The characterization analysis and experimental results confirmed that the composite material with TiO₂:BC=1:2 exhibited the highest overall ability to remove methyl orange（MO）,with good adsorption capacity and the superior photocatalytic activity compared to pure TiO₂.This indicates the synergistic effect of adsorption and photocatalysis,achieving a removal rate of 99.09%for high concentration methyl orange wastewater within 240 min.During the removal process,the biochar provided the adsorption capacity of the composite material,addressing the issue of TiO₂ nanoparticles prone to aggregation and enhancing the transfer ability of photogenerated electrons,laying the foundation for subsequent research.The problematic solid-liquid separation and low light utilization of traditional powder composites have hindered the industrial application prospect of adsorptive-photocatalytic technology.In this work,a lamellar hierarchically porous structured Sycamore-leaf TiO₂/biochar composite（LBT）was synthesized via a sol-hydrothermal method.The characterization results demonstrated that,compared with the pristine leaf biochar（LB）,the LBT exhibited enhanced specific surface area,pore volume,and adsorption sites.TiO₂ nanoparticles were uniform Ly distributed on the surface and within the multilevel pore structure of the obtained composite,featuring functional groups such as-OH,-COOH and Ti-O-C,which could provide increased active sites for the adsorptive-photocatalytic process.The pseudo-second-order,Weber-Morris intragranular diffusion,and Langmuir models could well describe the adsorption process for MO.LBT exhibited a high removal efficiency of 95.65%for MO under simulated sunlight,with a maximum adsorption capacity of 284.06 mg/g.The pollutants adhered to LBT were degraded by 74.17%during the synergistic action of adsorption-photocatalysis,thus allowing the composite to be recycled and reused.This work provides a viable application approach for the practical utilization of adsorptive-photocatalytic multifunctional materials to remove organic pollutants from water.