Pyrolysis temperature affects the physiochemical characteristics of lanthanum-modified biochar derived from orange peels: Insights into the mechanisms of tetracycline adsorption by spectroscopic analysis and theoretical calculations

Biochar (BC) derived from orange peels was modified using LaCl3 to enhance its tetracycline (TC) adsorption capacity. SEM-EDS, FT-IR, XRD, and BET were used to characterize the physiochemical characteristics of La-modified biochar (La-BC). Batch experiments were conducted to investigate the effects of several variables like pyrolysis temperature, adsorbent dosage, initial pH, and coexisting ions on the adsorption of TC by La-BC. XPS and density functional theory (DFT) were used to elucidate the TC adsorption mechanism of La-BC. The results demonstrated that La was uniformly coated on the surface of the La-BC. The physiochemical characteristics of La-BC highly depended on pyrolysis temperature. Higher temperature increased the specific surface area and functional groups of La-BC, thus enhancing its TC adsorption capacity. La-BC prepared at 700 degrees C (BC@La-700) achieved the maximum adsorption capacity of 143.20 mg/g, which was 6.8 and 4.6 times higher than that of BC@La-500 and BC@La-600, respectively. The mechanisms of TC adsorption by La-BC were most accurately described by the pseudo-second-order kinetic model. Furthermore, the adsorption isotherm of La-BC was consistent with the Freundlich model. BC@La-700 achieved good TC adsorption efficiencies even at a wide pH range (pH 4-10). Humic acid significantly inhibited TC adsorption by La-BC. The presence of coexisting ions (NH4+, Ca2+, NO3-) did not significantly affect the adsorption capacity of LaBC, particularly BC@La-700. Moreover, BC@La-700 also exhibited the best recycling performance, which achieved relative high adsorption capacity even after 5 cycles. The XPS results showed that pi-pi bonds, oxygen-containing

Automated summary

Biochar modified with LaCl3 from orange peels was used to enhance the adsorption of tetracycline. Different parameters such as pyrolysis temperature, adsorbent dosage, initial pH, and coexisting ions were investigated. The results showed that higher pyrolysis temperature increased the specific surface area and functional groups of the modified biochar, resulting in higher adsorption capacity. The La-BC prepared at 700 degrees C achieved the highest adsorption capacity. The adsorption mechanism followed the pseudo-second-order kinetic model and the adsorption isotherm was consistent with the Freundlich model. The presence of humic acid inhibited TC adsorption, while coexisting ions did not significantly affect the adsorption capacity, especially for BC@La-700.