From rice biomass to photocatalytically active silica-based microspheres for wastewater remediation

The increasing consumption rate of antibiotics is inevitably correlated to an enhancement of their concentration in wastewater, which consequently promotes antibiotic resistance. In this context, new materials able to efficiently degrade antibiotics, and possibly obtained by renewable resources via sustainable synthetic strategies, are needed. Following these requirements, the goal of this thesis is the preparation of a photocatalytically active microsystem for antibiotic remediation, which, unlike the state-of-the-art materials, is synthesized starting from rice husk biomass. The resulting SiO2 component (RHA) was implemented in the synthesis of silica-based microspheres with tailored interconnected porosity, substituting one silane precursor in different weight percentages (20%, 50%, 80%, 100%). Based on the physicochemical characterization data (optical microscopy, physisorption, zeta-potential analysis, TGA, FT-IR, NIR, SEM/EDS, ICP-OES, XRD and solid-state NMR), two modified microspheres, MSR100 and MSR100ht (heat treated at 900°C), were investigated as photocatalysts to degrade the antibiotic minocycline in a batch-type solar reactor and compared with non-modified microspheres. The photodegradation tests revealed that MS-RHA 100% h.t. has the best performance (78% degradation in 30 min against 18 % of non-modified microspheres), and maintained it over at least 4 recycling stages. In conclusion, this work demonstrates that bio-based SiO2 can be used for the preparation of stable and active photocatalysts.