The extraction of silica particles from rice husks has been extensively studied. This review aims to present the most efficient approach to harnessing rice husk biomass and converting silica into high-value-added materials for direct applications to address current challenges like water purification. Rice husks, as a residue from agriculture, had been largely used as a source of power through direct incineration in major rice-producing countries. However, rice husks present an intriguing opportunity as a renewable source of SiO₂, offering a low-cost adsorbent with a high surface area and ease of functionalization that can be transformed into diverse mesoporous silica structures or composites, enabling applications in catalysis, drug delivery, water treatment, etc. This dual potential of rice husks can be harnessed by combining bio-oil and syngas production through pyrolysis with the efficient extraction of SiO₂, ensuring the comprehensive utilization of the biomass. This review not only highlights the immense potential of silica nanoparticles but also serves as a roadmap for future investigations, with the ultimate aim of harnessing the full capabilities of this renewable and sustainable resource, contributing to the circular economy by yielding valuable by-products.

A protein-direct synthetic route to make nanobiohybrids containing copper nanoparticles (CuNPs) using an enzyme in combination with copper sulfate in aqueous media at room temperature is described. Enzyme–Cu(II) intermediates, rapidly generated in aqueous media, are transformed, induced by the enzyme structure, to facilitate the formation of a particular Cu species, tailoring the size of the nanoparticles formed depending on the experimental conditions, e.g. the pH, reducing step, amount of enzyme or incubation time. This controlled synthesis allows the preparation of tailor-made nanobiohybrids of Cu(0)NPs, Cu(0)/Cu₂ONPs, Cu₂ONPs or Cu₃(PO₄)₂NPs on the multimilligram scale. The catalytic performance of the novel CuNPs nanobiohybrids was evaluated in relation to the selective C–H functionalization of benzene via direct monohydroxylation using hydrogen peroxide as a green oxidant under mild conditions, in aqueous media and at moderate temperature. Optimization of the amount of hydrogen peroxide, the co-solvent, and the temperature was performed, resulting in the production of 17 mM phenol with 83% selectivity using the Cu-CALB-PHOS-NR nanobiohybrid as a catalyst.

This review describes the advances in the design and application of novel artificial metalloenzymes in C–H activation reactions.

Copper nanoparticles–enzyme biohybrid is a promising material for the remediation of contaminated waters, but its function is influenced by its effect on degradation organic pollutants. This study is the first investigation into the fast degradation of a high amount of Bisphenol A (BPA) in water at neutral pH and room temperature. Four different CuNPs biohybrids with different cu species and nanoparticle sizes were used as catalysts. The biohybrid CuNPs@CALB-3, which contained Cu₂O nanoparticles of around 10 nm size, showed excellent catalytic performance removing >95% BPA content (45 ppm) in an aqueous solution in 20 min in the presence of hydrogen peroxide at pH 8 using 1.5 g/L of a catalyst. The catalyst showed excellent stability and recyclability at these conditions.

The growing concern over water pollution and waste management requires innovative solutions that promote resource efficiency within a circular economy. This study aims to utilize rice husk (RH) as a sustainable feedstock to develop highly porous silica particles and generate valuable by-products, addressing the dual challenges of waste reduction and water contamination. We hypothesize that optimizing the production of amorphous silica from acid-washed RH will enhance its adsorptive properties and facilitate the concurrent generation of bio-oil and syngas. Amorphous silica particles were extracted from acid-washed RH with a yield of 15 wt% using a combination of acid washing at 100 °C, pyrolysis at 500 °C, and calcination at 700 °C with controlled heating at 2 °C/min. The optimized material (RH2-SiO₂), composed of small (60–200 nm) and large (50–200 µm) particles, had a specific surface area of 320 m²/g, with funnel-shaped pores with diameters from 17 nm to 4 nm and showed a maximum cadmium adsorption capacity of 407 mg Cd/g SiO₂. Additionally, the pyrolysis process yielded CO-rich syngas and bio-oil with an elevated phenolic content, demonstrating a higher bio-oil yield and reduced gas production compared to untreated RH. Some limitations were identified, including the need for bio-oil upgrading, further research into the application of RH2-SiO₂ for wastewater treatment, and the scaling-up of adsorbent production. Despite the challenges, these results contribute to the development of a promising adsorbent for water pollution control while enhancing the value of agricultural waste and moving closer to a circular economy model.