UV light-driven photocatalytic degradation of methylene blue with β-Ga2O3 nanoparticles conjugated to nanocellulose extracted from a biowaste fibre

β-Ga 2 O 3 NPs were synthesised hydrothermally and annealed at 1000°C. Citrate-capped nanocellulose fibres (CNCFs) were extracted from Azanza Garckeana fibres through sequential hydrolysis in 4.1% citric acid, which had been diluted from a lemon concentrate (pH < 1.5) and 2% NaOH. The best performing photocatalyst comprising a composite of β-Ga 2 O 3 NPs dispersed onto CNCFs with a 20% mass (β-Ga 2 O 3 /20% CNCFs) was used for the degradation of methylene blue (MB) at pH 9 and under a 365 nm ultraviolet light irradiation at a radiance of 106 mW cm −2 . The mean rate of MB degradation in the presence of β-Ga 2 O 3 /20% CNCFs was 14.1 (±0.5) x 10 −3 min −1, in 1.56 mM MB solution, and this was 2 times higher than for β-Ga 2 O 3, which had a rate constant of 7.8 (±0.4) x 10 −3 min −1 . The rates for both catalysts were slightly lower in a river water spiked at the same level. The β-Ga 2 O 3 /20% CNCFs NPs demonstrated good reusability and stability, allowing for up to 4 cycles, for which the degradation efficiency decreased only by < 20%. Radical capture with specific scavengers suggested positively charged holes (h + ), OH • , and O 2 •- as active species responsible for the photocatalytic redox degradation of MB. Mass spectra of intermittently sampled mixtures from the degradation process revealed the formation of sulphonated amino-phenyl aldehydes and amino-polyphenols as reaction intermediates. These intermediates are colourless, more environmentally benign. A 77% reduction in the chemical oxygen demand (COD) of a 1.56 mM MB spiked solution upon photodegradation for 3 h, together with the mass spectral data after the reaction, suggested the partial carbon mineralisation of MB to form water and dissolved carbon dioxide.