Modified Silica Nanoparticles from Rice Husk Supported on Polylactic Acid as Adsorptive Membranes for Dye Removal.

Industrial effluents and wastewater treatment have been a mainstay of environmental preservation and remediation for the last decade. Silica nanoparticles (SiO2) obtained from rice husk (RH) are an alternative to producing low-cost adsorbent and agriculture waste recovery. One adsorption challenge is facilitating the adsorbate separation and reuse cycle from aqueous medium. Thus, the present work employs SiO2 supported on polylactic acid (PLA) nanofibers obtained by the electrospinning method for Rhodamine B (RhB) dye adsorption. The silica surface was modified with trimethylsilyl chloride (TMCS) to increase affinity towards organic compounds. As a result, the silanized surface of the silica from rice husk (RHSil) promoted an increase in dye adsorption attributed to the hydrophobic properties. The PLA fibers containing 40% SiO2 (w w-1) showed about 85-95% capacity adsorption. The pseudo-first-order kinetic model was demonstrated to be the best model for PLA:SiO2 RHSil nanocomposites, exhibiting a 1.2956 mg g-1 adsorption capacity and 0.01404 min-1 kinetic constant (k1) value. In the reuse assay, PLA:SiO2 membranes preserved their adsorption activity after three consecutive adsorption cycles, with a value superior to 60%. Therefore, PLA:SiO2 nanocomposites from agricultural waste are an alternative to "low-cost/low-end" treatments and can be used in traditional treatment systems to improve dye removal from contaminated waters.

CuO nanoparticles decorated on hydroxyapatite/ferrite magnetic support: photocatalysis, cytotoxicity, and antimicrobial response.

Photocatalysts supported in magnetic nanocomposites for application in environmental remediation processes have been evaluated for removing contaminants due to easy recovery and low toxicity to the ecosystem. In this work, copper oxide (CuO) nanoparticles with photocatalytic properties were decorated on magnetic support constituted by hydroxyapatite (HAP) and ferrite to achieve efficiency in contaminated water remediation under visible light irradiation. First, nanomaterials were obtained by precipitation route, allowing fast and straightforward synthesis. Then, CuO nanoparticles with 6 nm diameter were efficiently decorated on magnetic support (25 nm), showing a high ability to absorb visible light irradiation (bandgap) to promote electronic transition and charge separation. Under visible irradiation, CuO promotes the H2O2 reduction in the conduction band (BC) to form hydroxyl radicals (•OH), which are responsible for rhodamine B (RhB) dye degradation (> 90% in 60 min). Magnetic hysteresis assays confirmed the magnetic properties of HAP/ferrite support, which enabled the recovery and reuse of the magnetic photocatalyst efficiently up to 3 cycles. Due to low Cu2+ leaching after the photocatalytic application stage, cytotoxicity assay for the Allium cepa seeds did not exhibit abnormal cells other than those commonly found. Furthermore, the CuO-decorated nanoparticles showed bactericidal activity against S. aureus (Gram-positive) and E. coli (Gram-negative) microorganisms, being more significant for the first one. Thus, the developed nanocomposite of CuO nanoparticles decorated on the magnetic support surface showed to be a complete system for water remediation, acting in contaminant degradation under visible light irradiation and bactericidal control with environmentally friendly characteristics.Graphical abstract CuO nanoparticles decorated on hydroxyapatite/ferrite magnetic support acting as a photocatalytic and bactericidal system.

Nb2O5 nanoparticles decorated with magnetic ferrites for wastewater photocatalytic remediation.

Nanotechnology has been studied on environmental remediation processes to foster greater photocatalysts efficiency and reuse in wastewater. This study investigated the photocatalytic efficiency and viability of niobium pentoxide (Nb2O5) nanoparticles decorated with magnetic ferrite (cobalt ferrite (CoFe2O4) or magnesium ferrite (MgFe2O4)) for atrazine photodegradation. Thus, the decorated Nb2O5 was synthesized by the polymeric precursor method, forming nanoparticles with sizes ranging from 25 to 50 nm. Nanocomposite elementary analyses showed a homogeneous distribution of elements on all particles surface. Efficient magnetic saturation was observed for pure CoFe2O4 (53 emu g-1) and MgFe2O4 (19 emu g-1) nanoparticles, promoting the magnetic removal of Nb2O5:CoFe2O4 and Nb2O5:MgFe2O4 nanocomposites. Photocatalytic assays showed 88% efficiency for atrazine photodegradation with all nanomaterials, which represented a 21% increase compared to photolysis in the 1st cycle. The magnetic nanocomposites when applied to a 5th cycle maintained the atrazine photodegradation activity. In this way, magnetic Nb2O5-based nanocomposites decorated with ferrite nanoparticles showed an efficient photocatalytic response, in addition to posterior magnetic removal from the aqueous medium. Therefore, the evaluated magnetic Nb2O5 nanocomposites may be an alternative to enhance the wastewater removal process and foster the reuse in advanced oxidative processes.

Evaluation of Photocatalytic Activity in Water Pollutants and Cytotoxic Response of α-Fe2O3 Nanoparticles.

α-Fe2O3 samples were manufactured by means of the polymeric precursor method. The powders were sintered and calcined at temperatures of 300-700 °C for 2 h, respectively. In the X-ray diffraction results, the formation of the rhombohedral phase without secondary phases was exhibited. The size of the particle increased after calcination at 700 °C, exhibiting a slightly more irregular morphology for the samples calcined with the addition of NH4OH in the synthesis process. From the field-emission scanning electron microscopy measurements, the particle size was determined, showing a smaller size for the samples without NH4OH in the synthesis process. The samples calcined at 600 °C had a size of 100 nm, with the sizes for lower temperatures being smaller. The size of the nanoparticle agglomerates was largest for the samples with NH4OH; however, the zeta potential was slightly lower over time for these samples. The phase study of the α-Fe2O3 nanoparticles was confirmed by means of Raman spectroscopy, without additional bands of another crystal structure. In addition, the synthesized nanoparticles exhibited good photocatalytic activity in the degradation of rhodamine B (RhB) and atrazine (ATZ) within 40 min, with a maximum degradation of 59% for ATZ and 40% for rhodamine. The best responses in the degradation were for the samples without the addition of NH4OH in the synthesis process and in proportions lower than 0.1 g. The cytotoxic effects of the nanoparticles obtained at 600 °C were evaluated in apical cells of onion roots. The results are promising for future applications because no changes were observed in the mitosis of the cells.