Surface Modification of Cured Inorganic Foams with Cationic Cellulose Nanocrystals and Their Use as Reactive Filter Media for Anionic Dye Removal

In this work, a surface cationized inorganic-organic hybrid foam was produced from porous geopolymer (GP) and cellulose nanocrystals (CNCs). GPs were synthesized from alkali-activated metakaolin using H₂O₂ as a blowing agent and hexadecyltrimethylammonium bromide (CTAB) as a surfactant. These highly porous GPs were combined at pH 7.5 with cationic CNCs that had been synthesized from dissolving pulp through periodate oxidation followed by cationization in a deep eutectic solvent. The GP-CNC hybrid foams were employed as reactive filters in the removal of the anionic dye, methyl orange (MO; 5-10 mg/L, pH 7). The effects of a mild acid wash and thermal treatments on the structure, properties, and adsorption capacity of the GPs with CNCs and MO were investigated. The CNCs aligned as films and filaments on the surfaces of the neutralized GPs and the addition of CNCs improved MO removal by up to 84% compared with the reference sample. In addition, CTAB was found to disrupt the attachment of CNCs on the pores and improve adsorption of MO in the GPs with and without CNCs.

Characterization and Mechanism for the Protection of Photolytic Decomposition of N-Halamine Siloxane Coatings by Titanium Dioxide

N-Halamine antibacterial materials have superior inactivation activities due to oxidative chlorine species. However, N-Cl bonds and bonds between N-halamine and substrates often decompose rapidly under UV irradiation, leading to unrecoverable loss of antimicrobial activity. In this study, titanium dioxide was covalently bonded onto N-halamine siloxane poly[5,5-dimethyl-3-(3'-triethoxysilylpropyl)hydantoin] (PSPH) via a sol-gel process. Experimental testing of the chlorinated cotton fabrics treated with TiO2/PSPH demonstrated that the residual oxidative chlorine in cotton-TiO2/PSPH-Cl was still effective for inactivating bacteria after 50 washing cycles and under UV light irradiation for 24 h. Quantum mechanical calculations found that TiO2 improves the UV stability of the PSPH-Cl system by increasing the activation barrier of the C-Si scission reaction responsible for the loss of the biocidal hydantoin moiety. SEM, XPS and FTIR spectra were used to characterize the coated cotton samples. Cotton-TiO2/PSPH-Cl samples exhibited good antibacterial activity against Staphylococcus aureus (ATCC 6538) and Escherichia coli O157:H7 (ATCC 43895). The storage stability and washing stability of treated cotton fabrics were also investigated.