Abstract
In this work, garden waste Clivia miniata leaves (CL) were used as a feedstock to produce high performance biochar (BCL-K-H) through the pretreatment processes of alkali hydrolysis combined with acid hydrolysis. Specifically, CL is subjected to a two-step pretreatment process to destroy its dense wood fibre structure, and then the pretreatment product is processed into biochar by carbonation activation. The results demonstrated that the physicochemical properties of the modified Clivia miniata leaves biochar (BCL-K-H) prepared by the pretreatment process were altered in comparison with those of Clivia miniata leaves biochar (BCL). The specific surface area increased from 3052.12 to 3555.31 m(2)/g, and the total pore volume increased from 1.94 to 2.91 cm(3)/g. The characterisation results demonstrated that the surface of BCL-K-H contained a significant number of reactive functional groups (e.g. hydroxyl, hydrocarbon and carboxyl groups, etc.), which may provide a substantial number of active sites during the adsorption of pollutants and enhance the adsorption performance. The pollutants tetracycline hydrochloride (TH) and synthetic dye Rhodamine B (RhB) were studied to gain insight into biochars' performance. The maximum adsorption capacity of BCL-K-H for pollutants was found to be 1436.56 mg/g (TH) and 1505.47 mg/g (RhB). The adsorption process of BCL-K-H on the pollutants was found to be in accordance with the proposed second-order kinetic model and the Freundlich isotherm model. This finding suggests that the adsorption process may involve electron transfer between the pollutant and the adsorbent, as well as adsorption on heterogeneous surfaces. The presence of a large number of reactive functional groups (e.g. hydroxyl, hydrocarbon and carboxyl groups, etc.) within the adsorbent material has been postulated to provide a substantial number of active sites during the adsorption of pollutants, thereby enhancing the adsorption performance. Following 10 cycles, the removal of pollutants by BCL and BCL-K-H remained above 60%. All data demonstrate that the pre-treatment of biomass precursors is effective and feasible in further improving the performance of biochar, thus providing a new strategy for the further development of lignocellulosic garden waste.