All-weather Ag–ZnO/cellulose photocatalysts tailored by surface groups and aspect ratios of cellulose nanofibers

Ag–ZnO/cellulose nanocomposites with an all-weather photocatalytic performance that responds to all light conditions (including ultraviolet light, visible light, and even darkness) were fabricated by adjusting the surface groups and aspect ratios of the cellulose nanofiber substrate. The cellulose nanofibers improved the dispersibility and photostability of the Ag–ZnO nanoparticles (NPs), thereby enhancing the photocatalytic activity. The morphologies and sizes of the ZnO and Ag NPs within the Ag–ZnO/cellulose nanocomposites were controlled by using cellulose nanofibers with different surface groups and aspect ratios. ZnO NPs with average diameters of 250, 500, and 100 nm were synthesized in situ using cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and TEMPO-mediated oxidized cellulose nanofibrils (TOCNFs), respectively. The Ag–ZnO/TOCNF nanocomposites exhibited excellent all-weather photocatalytic performance, high loading amounts, and large effective contact area with pollutants. Free radical trapping experiments demonstrated that ·OH had the most significant effect on the photocatalytic activity. The photocatalytic activity of the Ag–ZnO/TOCNF nanocomposites was improved by preventing the recombination of electrons and holes and increasing the contact area with pollutants and light. The photogenerated electrons stored on the surface of the ZnO NPs and Ag NPs were further used for reducing H 2 O 2 to generate ·OH free radicals in the dark, which continued to catalyze the degradation of pollutants without light irradiation. Moreover, the photocatalytic degradation of methyl orange to CO 2 and H 2 O was confirmed via a catalytic mechanism and liquid chromatography–mass spectrometry.