Laccase immobilization and surface modification of activated carbon fibers by bio-inspired poly-dopamine

Preparation and Immobilization Mechanism on a Novel Composite Carrier PDA-CF/PUF to Improve Cells Immobilization and Xylitol Production

The preparation of a novel composite carrier of polydopamine-modified carbon fiber/polyurethane foam (PDA-CF/PUF) was proposed to improve cell immobilization and the fermentation of xylitol, which is an important food sweetener and multifunctional food additive. Candida tropicalis was immobilized on the composite carrier by adsorption and covalent binding. The properties and immobilization mechanism of the composite carrier and its effect on immobilized cells were investigated. It showed that the modification of PDA enhanced the loading of CF on the PUF surface and the adhesion of cells on the composite carrier surface. Also, the biocompatibility of carriers to cells was improved. In addition, the introduction of PDA increased the active groups on the surface of the carrier, enhanced the hydrophilicity, promoted the cells immobilization, and increased the xylitol yield. It was also found that expression of the related gene XYL1 in cells was significantly increased after the immobilization of the PDA-CF/PUF composite carrier during the fermentation. The PDA-CF/PUF was an immobilized carrier with the excellent biocompatibility and immobilization performance, which has great development potential in the industrial production of xylitol.

Laccase immobilization and its degradation of emerging pollutants: A comprehensive review

The chronic lack of effective disposal of pollutants has resulted in the detection of a wide variety of EPs in the environment, with concentrations high enough to affect ecological health. Laccase, as a versatile oxidase capable of catalyzing a wide range of substrates and without producing toxic by-products, is a potential candidate for the biodegradation of pollutants. Immobilization can provide favorable protection for free laccase, improve the stability of laccase in complex environments, and greatly enhance the reusability of laccase, which is significant in reducing the cost of industrial applications. This study introduces the properties of laccase and subsequently elaborate on the different support materials for laccase immobilization. The research advances in the degradation of EDs, PPCPs, and PAHs by immobilized laccase are then reviewed. This review provides a comprehensive understanding of laccase immobilization, as well as the advantages of various support materials, facilitating the development of more economical and efficient immobilization systems that can be put into practice to achieve the green degradation of EPs.

The controlled degradation of bacterial cellulose in simulated physiological environment by immobilization and release of cellulase

Bacterial cellulose (BC) has good network structure, biocompatibility, and excellent mechanical properties, and is widely used in the field of biomaterials. The controllable degradation of BC can further broaden its application. Oxidative modification and cellulases may endow BC with degradability, but these methods inevitably lead to the obvious reduction of its initial mechanical properties and uncontrolled degradation. In this paper, the controllable degradation of BC was realized for the first time by using a new controlled release structure that combines the immobilization and release of cellulase. The immobilized enzyme has higher stability and is gradually released in the simulated physiological environment, and its load can control the hydrolysis rate of BC well. Furthermore, the BC-based membrane prepared by this method retains the favorable physicochemical performance of the original BC, including flexibility and great biocompatibility, and holds good application prospects in drug control release or tissue repair.

Bactericidal and biocatalytic temperature responsive microgel based self-cleaning membranes for water purification

The present study focuses on creating an antimicrobial and biocatalytic smart gating membrane by synthesizing unique core-shell microgels. The core-shell microgels are synthesized by grafting short chains of poly(ethylenimine) (PEI) onto a poly((N-isopropyl acrylamide)-co-glycidyl methacrylate)) (P(NIPAm-co-GMA)) core. Subsequently, the produced microgels are utilized as a substrate for synthesizing and stabilizing silver nanoparticles (Ag NPs) through an in-situ approach. These Ag NPs immobilized microgels are then suction filtered over a polyethylene terephthalate (PET) track-etched support to create cross-linked composite microgel membranes (CMMs). After structural and permeation characterization of the prepared CMMs, the laccase enzyme is then covalently grafted to the surface of the membrane and tested for its effectiveness in degrading Reactive red-120 dye. The laccase immobilized biocatalytic CMMs show effective degradation of the Reactive red-120 by 71%, 48%, and 34% at pH 3, 4, and 5, respectively. Furthermore, the immobilized laccase enzyme showed better activity and stability in terms of thermal, pH, and storage compared to the free laccase, leading to increased reusability. The unique combination of Ag NPs and laccase on a thermoresponsive microgel support resulted in a responsive self-cleaning membrane with excellent antimicrobial and dye degradation capabilities for environmentally friendly separation technology.

A Cu(II) MOF with laccase-like activity for colorimetric detection of 2,4-dichlorophenol and p-nitrophenol

Metal-organic framework (MOF) materials with aqueous stability have a good potential application in the field of mimetic enzymes. However, most of them have poor robustness in aqueous solution due to competitive coordination effects between water molecules and central metal ions. Herein, a copper-based MOF (Cu-SM MOF) was prepared using copper ions and 5-(sulfomethyl) isophthalic acid (5-SMIPA) by a hydrothermal process. Considering the similarity of coordination and morphology with HKUST-1, the aqueous stability and laccase-like activity of the Cu-SM MOF were investigated using HKUST-1 as the reference. The Cu-SM MOF shows superior aqueous stability to HKUST-1 after immersion in buffer solutions, especially under alkaline conditions. Moreover, the Cu-SM MOF possesses higher catalytic activity than HKUST-1 at a high salt concentration, high temperature, etc., because the Cu-SM MOF exhibits lower K_m and higher V_max values than those of laccase and reported mimetic enzymes. The mimetic enzyme behavior of the Cu-SM MOF is demonstrated in the oxidation of phenols, as well as in the detection of 2,4-dichlorophenol (2,4-DP) and p-nitrophenol with linear ranges of 1-100 μM and 2-250 μM, and limits of detection of 0.53 μM and 1.62 μM, respectively. Owing to the excellent aqueous stability and laccase-like activity of the Cu-SM MOF, it has great application prospects in many fields, such as the determination of phenols and the treatment of industrial wastewater.

New liquid supports in the development of integrated platforms for the reuse of oxidative enzymes and polydopamine production

Polydopamine (PDA), a bioinspired polymer from mussel adhesive proteins, has attracted impressive attention as a novel coating for (nano) materials with an adequate conformal layer and adjustable thickness. Currently, PDA is obtained from dopamine chemical oxidation under alkaline conditions, limiting its use in materials sensible to alkaline environments. Envisaging a widespread use of PDA, the polymerization of dopamine by enzymatic catalysis allows the dopamine polymerization in a large range of pHs, overcoming thus the limitations of conventional chemical oxidation. Moreover, the conventional method of polymerization is a time-consuming process and produces PDA films with poor stability, which restricts its applications. On the other hand, the main bottleneck of enzyme-based biocatalytic processes is the high cost of the single use of the enzyme. In this work, laccase was used to catalyse dopamine polymerization. To improve its performance, a liquid support for integrating the laccase and its reuse together with the PDA production and recovery was developed using aqueous biphasic systems (ABS). Firstly, dopamine polymerization by laccase was optimized in terms of pH, temperature and initial dopamine concentration. It was demonstrated that the highest enzymatic polymerization of dopamine was achieved at pH 5.5, 30°C and 2 mg ml−1 of dopamine. Then, ABS composed of polymers, salts and ionic liquids were evaluated to optimize the laccase confinement in one phase while PDA is recovered in the opposite phase. The most promising ABS allowing the separation of laccase from the reaction product is composed of polypropylene glycol (400 g mol−1) and K2HPO4. The polymerization of dopamine in ABS leads to a remarkable improvement of polymerization of 3.9-fold in comparison to the conventional chemical PDA polymerization. The phase containing the confined laccase was reused for four consecutive reaction cycles, with a relative polymerization of 68.9% in the last cycle. The results of this work proved that ABS are a promising approach to create a liquid support for enzyme reuse allowing the process intensification efforts. The use of biocatalysts in ABS emerges as sustainable and alternative platforms from environmental and techno-economic points of view.

Bioremoval of estrogens by laccase immobilized onto polyacrylonitrile/polyethersulfone material: Effect of inhibitors and mediators, process characterization and catalytic pathways determination

The presence of micropollutants in water, wastewater and soil are a global problem due to their persistent effect on ecosystems and human health. Although there are many methods of removal of environmental pollutants, they are often ineffective for degradation of pharmaceuticals, including estrogens. In presented work we proposed fabrication of electrospun material from polyacrylonitrile/polyethersulfone (PAN/PES) as a support for laccase immobilization by covalent binding. Oxidoreductase was attached to the electrospun fibers using polydopamine as a linker and produced system was used for degradation of two estrogens: 17β-estradiol (E2) and 17α-ethynylestradiol (EE2). It was shown that 92% of E2 and 100% of EE2 were degraded after 24 h of the process. Moreover, the effect of surfactants, metal ions and mediators on conversion efficiencies of estrogens was investigated and it was confirmed that immobilized enzyme possessed higher resistance to inhibitory agents as well as thermal and storage stability, compared to its native form. Finally, estrogenic activities of E2 and EE2 solutions decreased around 99% and 87%, respectively, after enzymatic conversion, that corresponds to significant reduction of the total organic carbon and formation of low-toxic final products of estrogens degradation.

Recent Developments in the Immobilization of Laccase on Carbonaceous Supports for Environmental Applications - A Critical Review

Τhe ligninolytic enzyme laccase has proved its potential for environmental applications. However, there is no documented industrial application of free laccase due to low stability, poor reusability, and high costs. Immobilization has been considered as a powerful technique to enhance laccase's industrial potential. In this technology, appropriate support selection for laccase immobilization is a crucial step since the support could broadly affect the properties of the resulting catalyst system. Through the last decades, a large variety of inorganic, organic, and composite materials have been used in laccase immobilization. Among them, carbon-based materials have been explored as a support candidate for immobilization, due to their properties such as high porosity, high surface area, the existence of functional groups, and their highly aromatic structure. Carbon-based materials have also been used in culture media as supports, sources of nutrients, and inducers, for laccase production. This study aims to review the recent trends in laccase production, immobilization techniques, and essential support properties for enzyme immobilization. More specifically, this review analyzes and presents the significant benefits of carbon-based materials for their key role in laccase production and immobilization.

Modification of Silica Xerogels with Polydopamine for Lipase B from Candida antarctica Immobilization

Silica xerogels have been proposed as a potential support to immobilize enzymes. Improving xerogels’ interactions with such enzymes and their mechanical strengths is critical to their practical applications. Herein, based on the mussel-inspired chemistry, we demonstrated a simple and highly effective strategy for stabilizing enzymes embedded inside silica xerogels by a polydopamine (PDA) coating through in-situ polymerization. The modified silica xerogels were characterized by scanning and transmission electron microscopy, Fourier tranform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and pore structure analyses. When the PDA-modified silica xerogels were used to immobilize enzymes of Candida antarctica lipase B (CALB), they exhibited a high loading ability of 45.6 mg/gsupport, which was higher than that of immobilized CALB in silica xerogels (28.5 mg/gsupport). The immobilized CALB of the PDA-modified silica xerogels retained 71.4% of their initial activities after 90 days of storage, whereas the free CALB retained only 30.2%. Moreover, compared with the immobilization of enzymes in silica xerogels, the mechanical properties, thermal stability and reusability of enzymes immobilized in PDA-modified silica xerogels were also improved significantly. These advantages indicate that the new hybrid material can be used as a low-cost and effective immobilized-enzyme support.

Optimization and efficacy studies of Laccase immobilized on Zein-Polyvinyl pyrrolidone nano fibrous membrane in decolorization of Acid Red 1

Azo dyes are widely used in textile industries. A significant portion of these recalcitrant dyes are being discharged to the natural waters. Due to their low biodegradability they pose serious pollution problems if untreated. In this work, decolourization studies of Acid Red 1 (AR1) by laccase enzyme immobilized onto zein-polyvinyl pyrrolidone (PVP) composite nanofiber is done. The nanofibers were characterized by scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) analysis. pH and temperature profiles of immobilized enzyme were found to be broader than its free counterpart. The K_m value was found to be 0.243 mM for free laccase and 0.958 mM for immobilized laccase. Similarly, V_max for the free enzyme was 3.572 U/mg compared to 2.48 U/mg of immobilized laccase. The relative activity of immobilized laccase was 64.91% after storage for 30 days at room temperature while it was 28.64% for free laccase. The temperature and pH for AR 1 decolorization were optimized and was found to be 60 °C and 5, respectively. Also, decolorization percentage was found to be 91.67% for immobilized laccase and 72.03% of free laccase in the presence of natural mediators like vanillin. From phytotoxicity studies it was found that the germination rate, shoot and root length was increased compared to untreated dye. Therefore, zein-PVP nanofiber immobilized laccase could be an ideal candidate for the textile dye decolorization.

Enhancement of laccase immobilization onto wet chitosan microspheres using an iterative protocol and its potential to remove micropollutants

This study was focused on creating a new and effective immobilization method for Trametes versicolor laccase (Lc) by using chitosan (CS) microspheres activated with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride. The activation of the support alternated with immobilization of the enzyme, in repetitive procedures, led to obtaining three different products. Also, the physicochemical properties of the new products were investigated and compared with those of free laccase. The discoloration and reusability properties of the immobilized Lc were evaluated using indigo carmine (IC) as a model micropollutant. The ESEM and FT-IR methods demonstrated that the Lc was successfully immobilized. The relative reaction rate and the total amount of immobilized Lc were tripled using the iterative protocol as proved by specific and Bradford assays. The maximum amount of immobilized Lc was 8.4 mg Lc/g CS corresponding to the third immobilization procedure. Compared to the free Lc, the operational stability of the immobilized Lc was significantly improved, presenting a maximum activity plateau over a pH range of 3-5 and a temperature range of 25-50 °C. The thermal inactivation study at 55 °C proved that the immobilized enzyme is three times more stable than the free Lc. The isoconversional and Michaelis-Menten methods showed that the immobilization did not affect the enzyme catalytic properties. After 32 days of storage, the residual activities are 85% for the immobilized laccase and 40% for the free one. In similar conditions, the free and immobilized Lc (2.12 x 10^-6 M) completely decolorized IC (7.15 x 10^-5 M) within 14 min. The immobilized Lc activity remained almost constant (80%) during 10 reusability cycles. All these results highlight the substantial advantages of the new immobilization protocol and demonstrate that immobilized Lc can be used as a promising micropollutant removal from real wastewater.

Electrospun poly(methyl methacrylate)/polyaniline fibres as a support for laccase immobilisation and use in dye decolourisation

Novel electrospun poly(methyl methacrylate)/polyaniline electrospun fibres were produced, characterised, modified, and used as a support for laccase immobilisation by two methods: adsorption and covalent binding. Effective deposition of laccase by both methods was confirmed by FTIR and CLSM results. Nevertheless, the main objective of the study was to select the most favourable immobilisation conditions and prepare heterogeneous biocatalysts with the best possible catalytic properties. The highest relative activity of enzymes immobilised by adsorption and covalent binding were obtained after 1 h of immobilisation using laccase solution at a concentration of 1 mg/mL, at pH 5 and 25 °C. It was found that the immobilised enzymes, which were present in amounts of 110 mg/g and 185 mg/g for systems with adsorbed and covalently bonded laccase respectively, exhibited slightly lower substrate affinity, and in consequence also a lower maximum reaction rate, than the free enzyme. The stability of laccase improved significantly upon immobilisation: both heterogeneous biocatalysts retained over 80% relative activity even after 10 repeated catalytic cycles and 30 days of storage. The obtained systems were used for decolourisation of Remazol Brilliant Blue R dye from a model aqueous solution, resulting in removal efficiencies of 87% and 58% using adsorbed and covalently bonded laccase, respectively. The described approach to the removal of textile dye from model solution is significant for the sustainable and environmentally friendly decolourisation of various compounds from wastewater.

Amino-modified kraft lignin microspheres as a support for enzyme immobilization

In this research, it has been demonstrated that amino-modified microspheres (A-LMS) based on bio-waste derived material, such as kraft lignin, have good prospects in usage as a support for enzyme immobilization, since active biocatalyst systems were prepared by immobilizing β-galactosidase from A. oryzae and laccase from M. thermophila expressed in A. oryzae (Novozym® 51003) onto A-LMS. Two types of A-LMS were investigated, with different emulsifier concentrations (5 wt% and 10 wt%), and microspheres produced using 5 wt% of emulsifier (A-LMS_5) showed adequate pore shape, size and distribution for enzyme attachment. The type of interactions formed between enzymes (β-galactosidase and laccase) and A-LMS_5 microspheres demonstrated that β-galactosidase is predominantly attached via electrostatic interactions while attachment of laccase is equally governed by electrostatic and hydrophobic interactions. Furthermore, the A-LMS_5-β-galactosidase exhibited specificity towards recognized prebiotics (galacto-oligosaccharides (GOS)) synthesis with 1.5-times higher GOS production than glucose production, while for environmental pollutant lindane degradation, the immobilized laccase preparation exhibited high activity with a minimum remaining lindane concentration of 22.4% after 6 days. Thus, this novel enzyme immobilization support A-LMS_5 has potential for use in green biotechnologies.

The active biocatalyst systems were developed by immobilizing β-galactosidase from A. oryzae and laccase from M. thermophila expressed in A. oryzae (Novozym®51003) onto amino-modified microspheres based on bio-waste derived material, such as kraft lignin.

Adsorptive removal of adsorbable organic halogens by activated carbon

Current research mainly focuses on the reduction of adsorbable organic halogen (AOX) sources, while studies on AOX monitoring and management in the environment are scarce. Organic pollutants in water are mainly fixed by sediments. Thus, in this paper, activated carbon was used to simulate the adsorption of AOX by sediments. AOX volatilization and degradation were also studied to exclude their effect on adsorption. Micromolecule chlorides were more easily volatilized and degraded than chlorobenzene and chlorophenol. The adsorption of activated carbon to AOX in bleaching wastewater was also studied and the optimum conditions for AOX removal were elucidated (particle size, 62 µm; time, 120 min; pH, 2.5; temperature, 40°C; and activated carbon dosage, 1.75 g l-1). AOX adsorption by activated carbon is a chemical process. Hence, the chemical compositions of the bleaching effluent with and without adsorption were analysed by GC-MS. The results revealed that activated carbon exhibits a good AOX removal effect, thereby providing a theoretical basis for monitoring the AOX distribution in the environment.

Preparation and photocatalytic activity characterization of activated carbon fiber-BiVO4 composites

Herein, we describe the hydrothermal immobilization of BiVO₄ on activated carbon fibers (ACFs) and characterize the obtained composite by several instrumental techniques, using Reactive Black KN-B (RB5) as a model pollutant for photocatalytic performance evaluation and establishing the experimental conditions yielding maximal photocatalytic activity. The photocatalytic degradation of RB5 is well fitted by a first-order kinetic model, and the good cycling stability and durability of BiVO₄@ACFs highlight the potential applicability of the proposed composite. The enhanced photocatalytic activity of BiVO₄@ACFs compared to those of BiVO₄ and ACFs individually was mechanistically rationalized, and the suggested mechanism was verified by ultraviolet-visible spectroscopy, attenuated total reflectance Fourier-transform infrared spectroscopy, and RB5 degradation experiments. Thus, this work contributes to the development of BiVO₄@ACF composites as effective photocatalysts for environmental remediation applications.

Herein, we describe the hydrothermal immobilization of BiVO₄ on activated carbon fibers, using Reactive Black KN-B photocatalytic performance evaluation and establishing the experimental conditions yielding maximalphotocatalytic activity.