Abstract
Environmental concerns, along with oil shortages, have increased industrial interest in biomass conversion to produce biofuels and other valuable chemicals. A green option in biomass processing is the use of enzymes, such as cellulases, hemicellulases, and ligninolytic (laccase and peroxidases), which have outstanding specificity toward their substrates and can be reused if immobilized onto magnetic nanocarriers. Numerous studies report the biocatalysts’ performance after covalent binding or adsorption on differently functionalized magnetic nanoparticles (MNPs). Functionalization strategies of MNPs include silica-based surfaces obtained through a sol–gel process, graphene oxide-based nanocomposites, polymer-coated surfaces, grafting polymer brushes, and others, which have been emphasized in this review of the immobilization and co-immobilization of enzymes used for biomass conversion. Careful analysis of the parameters affecting the performance of enzyme immobilization for new hybrid matrices has enabled us to achieve wider tolerance to thermal or chemical stress by these biosystems during saccharification. Additionally, it has enabled the application of immobilized laccase to remove toxic organic compounds from lignin, among other recent advances addressed here related to the use of reusable magnetic carriers for bioderived chemical manufacturing.
Highlights
Biological processes stand out for their specificity and low environmental impact, but the application of enzymes on an industrial scale requires strategies to guide bioconversions practically and cost-effectively
A biorefinery consists of biomass processing, which can be performed by three different approaches: thermochemical conversion, first-generation conversion related to food derivatives, and second-generation conversion based on lignocellulosic biomass and food waste (Figure 1)
magnetic nanoparticles (MNPs) are sensitive to oxidation in an acidic medium and might aggregate, losing their superparamagnetic properties, so a polymer coating is usually performed using chitosan, polyvinyl alcohol (PVA), and grafting with polyacrylic acid (PAA)
Summary
Biological processes stand out for their specificity and low environmental impact, but the application of enzymes on an industrial scale requires strategies to guide bioconversions practically and cost-effectively. The synthesis of magnetic nanoparticles (Figure 2) is one of the most challenging process stages It determines the shape, particle size, and composition of the surface, defining its magnetic properties. MNPs are sensitive to oxidation in an acidic medium and might aggregate, losing their superparamagnetic properties, so a polymer coating is usually performed using chitosan, polyvinyl alcohol (PVA), and grafting with polyacrylic acid (PAA) Another route is based on silica gel-mediated organic synthesis. Different organic or inorganic coating, grafting, or condensation approaches are described, highlighting the importance of surface functionalization of MNPs to provide the surface with active groups These functional groups are used in enzyme immobilization by forming covalent bonds or physical adsorption, yielding reusable magnetic biocatalysts [15]. Superparamagnetic nanoparticles (MNPs) usually present average sizes in the 10–40 nm range along with a highlighted magnetic moment. For a more in-depth study of magnetic nanoparticle characterization, the reader is referred to [9,25,26]
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