Density functional theory for selecting modifiers for enhanced adsorption of tetracycline in water by biochar

Antibiotics and their metabolic byproducts are found in wastewater and natural water as a result of increased consumption,posing a major threat to humans and other living organisms.One of the most promising methods for their removal is adsorption using biochar because it offers excellent adsorption potential and is both affordable and environmentally beneficial.However,raw biochar frequently has a low adsorption capacity due to its limited pore structure and unfavorable surface characteristics.Biochar surface modifications using modifiers such as H3PO4,KOH,and NaOH have improved the surface area and thereby the adsorption capacity.Experimental methods for assessing the effectiveness and adsorption mechanism of modified biochar are costly and time-consuming.Density functional theory(DFT)was used to investigate the interfacial interactions and adsorption mechanism of tetracycline(TC),a widely used antibiotic for personal care and veterinary medication,on unmodified and modified biochar.The DFT calculations showed that the adsorption energy of TC on unmodified and modified biochar is in the following order:KOH-modified biochar(−2.38 eV)<NaOH-modified biochar(−2.20 eV)<unmodified biochar(−1.56 eV)<H3PO4-modified biochar(5.48 eV).The lower adsorption energy is associated with a stronger and more stable interaction between the adsorbent and the contaminant.This suggests that the adsorption of TC on KOH-modified biochar is more prolific and stable compared to the other biochar.This study provides an understanding of the mechanism underlying the adsorption of TC by modified biochar and can be used as a guide to screen for biochar with promising adsorption potential prior to experimental efforts.

Electronic-property dependent interactions between tetracycline and graphene nanomaterials in aqueous solution

Understanding the interactions between graphene nanomaterials（GNMs） and antibiotics in aqueous solution is critical to both the engineering applications of GNMs and the assessment of their potential impact on the fate and transport of antibiotics in the aquatic environment. In this study, adsorption of one common antibiotic, tetracycline, by graphene oxide（GO） and reduced graphene oxide（RGO） was examined with multi-walled carbon nanotubes（MWCNTs） and graphite as comparison. The results showed that the tetracycline adsorption capacity by the four selected carbonaceous materials on the unit mass basis followed an order of GO ＆gt; RGO ＆gt; MWCNTs ＆gt; graphite. Upon normalization by surface area,graphite, RGO and MWCNTs had almost the same high tetracycline adsorption affinity while GO exhibited the lowest. We proposed π-electron-property dependent interaction mechanisms to explain the observed different adsorption behaviors. Density functional theory（DFT） calculations suggested that the oxygen-containing functional groups on GO surface reduced its π-electron-donating ability, and thus decreased the π-based interactions between tetracycline and GO surface. Comparison of adsorption efficiency at different p H indicated that electrostatic interaction also played an important role in tetracycline-GO interactions. Site energy analysis confirmed a highly heterogeneous distribution of the binding sites and strong tetracycline binding affinity of GO surface.