Sustainable co-production of carbon quantum dots and activated carbon from natural rubber latex for the inhibition of pathogenic microorganisms and removal of pharmaceutical residues

Abstract

This study demonstrates a sustainable and integrated method for the co-production of carbon quantum dots (CQDs) and activated carbon (AC) using natural rubber (NR) latex, which is a renewable and widely available biomass. CQDs were synthesized via a hydrothermal method using cetyltrimethylammonium bromide and nitric acid as nitrogen dopants. The as-formed product comprised uniform amorphous nanoparticles (3.5–11.0 nm) that exhibited intense blue photoluminescence and abundant surface amino and oxygen-containing groups. The CQDs exhibited excellent antimicrobial and antiviral activities, achieving >99.9% inactivation of Staphylococcus aureus, Micrococcus luteus, Escherichia coli, Candida albicans, Aspergillus niger, and influenza A virus (H3N2) within 5 min of exposure at a concentration of 15 µg mL⁻¹. Moreover, they demonstrated negligible cytotoxicity toward HaCaT keratinocytes. Furthermore, the hydrochar obtained as a by-product of hydrothermal synthesis was subsequently converted into AC via physical and chemical activation, yielding a large-surface-area adsorbent (up to 1167 m² g⁻¹) featuring a diclofenac uptake capacity of 126.82 mg g⁻¹ at 25 °C. The adsorption process followed pseudo-second-order kinetics and a Langmuir-type monolayer adsorption mechanism. Adsorption mainly proceeded via π–π interactions, hydrogen bonding, and electrostatic attraction between diclofenac molecules and heteroatom-rich surface sites. This dual-function valorization of NR latex simultaneously addresses microbial and pharmaceutical pollution, advancing circular bioeconomy principles and offering sustainable solutions for water treatment and healthcare applications.