Nd:ZnS@GO nanotubes: a novel adsorbent cum photocatalyst for efficient removal of antibiotics and dyes from wastewater†

Herein, we designed a novel scaffold of graphene oxide (GO) nanotubes via coating of bimetallic neodymium-doped ZnS (Nd:ZnS@GO) for the potential removal of antibiotics and organic fluorescent dyes (OFDs) from wastewater. The GO nanosheets were transformed into nanotubes by unequal charge distribution, which tended them to align in order to minimize surface strain. Nd:ZnS@GO was deployed for fast adsorptive removal of antibiotics and complete photocatalytic degradation (PCD) of OFDs. Nd:ZnS@GO demonstrated superior scavenging efficiency (960 mg g⁻¹ for tetracycline and 1117.76 mg g⁻¹ for oxytetracycline) compared with previously reported metal-based nanocomposites. The adsorption process followed pseudo-first-order kinetics and the Freundlich isotherm model for both the antibiotics. Benefitting from its fast kinetics, Nd:ZnS@GO could remove pollutants for up to five cycles without losing its adsorption efficiency. The exceptional adsorption capacity was mainly attributed to non-covalent interactions, such as hydrogen bonding, π–π stacking, and cation–π bonding. After adsorption, Nd:ZnS@GO was regenerated and further used for the PCD of tetracycline (TC), oxytetracycline (OTC), methylene blue (MB), brilliant blue-green (BBG), brilliant blue-red (BBR), methyl orange (MO), and quinonoid phenolphthalein (QHIn). This study reveals the synthesis of GO nanotubes as promising and effective adsorbents cum photocatalysts for the adsorption and PCD of OFDs and antibiotics for the first time.