Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.

Renewable biowaste-derived carbon dots have garnered immense interest owing to their exceptional optical, fluorescence, chemical, and environmentally friendly attributes, which have been exploited for the detection of metals, non-metals, and organics in the environment. In the present study, water-soluble fluorescent carbon dots (CDs) were synthesized via facile green microwave pyrolysis of pine-cone biomass as precursors, without any chemical additives. The synthesized fluorescent pine-cone carbon dots (PC-CDs) were spherical in shape with a bimodal particle-size distribution (average diameters of 15.2 nm and 42.1 nm) and a broad absorption band of between 280 and 350 nm, attributed to a π-π* and n-π* transition. The synthesized PC-CDs exhibited the highest fluorescent (FL) intensity at an excitation wavelength of 360 nm, with maximum emission of 430 nm. The synthesized PC-CDs were an excellent fluorescent probe for the selective detection of Cu²⁺ in aqueous solution, amidst the presence of other metal ions. The FL intensity of PC-CDs was exceptionally quenched in the presence of Cu²⁺ ions, with a low detection limit of 0.005 μg/mL; this was largely ascribed to Cu²⁺ ion binding interactions with the enriched surface functional groups on the PC-CDs. As-synthesized PC-CDs are an excellent, cost effective, and sensitive probe for detecting and monitoring Cu²⁺ metal ions in wastewater.

Succinic acid is well established as bio-based platform chemical with production quantities expecting to increase exponentially within the next decade. Actinobacillus succinogenes is by far the most studied wild organism for producing succinic acid and is known for high yield and titre during production on various sugars in batch culture. At low shear conditions continuous fermentation with A. succinogenes results in biofilm formation. In this study, a novel shear controlled fermenter was developed that enabled: 1) chemostat operation where self-immobilisation was opposed by high shear rates and, 2) in-situ removal of biofilm by increasing shear rates and subsequent analysis thereof. The volumetric productivity of the biofilm fermentations were an order of magnitude more than the chemostat runs. In addition the biofilm runs obtained substantially higher yields. Succinic acid to acetic acid ratios for chemostat runs were 1.28±0.2 g.g−1, while the ratios for biofilm runs started at 2.4 g.g−1 and increased up to 3.3 g.g−1 as glucose consumption increased. This corresponded to an overall yield on glucose of 0.48±0.05 g.g−1 for chemostat runs, while the yields varied between 0.63 g.g−1 and 0.74 g.g−1 for biofilm runs. Specific growth rates (μ) were shown to be severely inhibited by the formation of organic acids, with μ only 12% of μmax at a succinic acid titre of 7 g.L−1. Maintenance production of succinic acid was shown to be dominant for the biofilm runs with cell based production rates (extracellular polymeric substance removed) decreasing as SA titre increases. The novel fermenter allowed for an in-depth bioreaction analysis of A. succinogenes. Biofilm cells achieve higher SA yields than suspended cells and allow for operation at higher succinic acid titre. Both growth and maintenance rates were shown to drastically decrease with succinic acid titre. The A. succinogenes biofilm process has vast potential, where self-induced high cell densities result in higher succinic acid productivity and yield.

This study describes the preparation of zinc oxide nanocomposite and its application as photocatalyst in the degradation of methylene blue under sunlight irradiation. Zinc oxide-coated biochar (ZnO/BC) nanocomposite was prepared using the hydrothermal method from banana peels and zinc acetate dihydrate as precursors. The biochar (BC), ZnO nanoparticles (ZnONPs), and ZnO/BC nanocomposite were characterized, and the results showed that ZnONPs had definite crystallinity and a regular surface morphology, with particles approximately 18 nm in size, and a XRD pattern corresponding to ZnONPs. In contrast, the ZnO/BC nanocomposite exhibited a more amorphous structure consistent with wurtzite (ZnO) and an irregular surface morphology with clusters of white particles measuring around 20–30 nm. Tauc’s plot was used to calculate the band gaps energy of ZnONPs (3.04 eV) and ZnO/BC nanocomposite (2.89 eV). Catalyst-free, ZnONPs, and ZnO/BC nanocomposite were utilized for the photocatalytic degradation of methylene blue (MB) under sunlight irradiation for 0 to 120 min in which ZnO/BC nanocomposite showed excellent photocatalytic degradation of MB under sunlight irradiation at 0 to 120 min due to lower band gap energy and synergetic effect between ZnO and BC. Dosages of 100 mg (ZnO/BC nanocomposite) and 10 ppm (MB) were optimized to obtain the best photocatalytic degradation efficiency (92 %) under sunlight irradiation with 0 to 120 min. The process was conducted with various parameters like dosage variation, concentration of MB, and different pH 3, 5, 8, and 10 to improve the photocatalytic degradation of MB from wastewater. The results indicated that the optimal conditions for the photocatalytic degradation of MB (92% after 120 min) were a catalyst dosage of 100 mg, an MB concentration of 10 ppm, and a pH of 10. This work demonstrates the potential of ZnO/BC nanocomposite photocatalyst for application in wastewater treatment and environment remediation.