Fabrications and applications of hemicellulose-based bio-adsorbents

Renewable hemicellulose-based materials for value-added applications

The importance of renewable resources and environmentally friendly materials has grown globally in recent time. Hemicellulose is renewable lignocellulosic materials that have been the subject of substantial valorisation research. Due to its distinctive benefits, including its wide availability, low cost, renewability, biodegradability, simplicity of chemical modification, etc., it has attracted increasing interest in a number of value-added fields. In this review, a systematic summarizes of the structure, extraction method, and characterization technique for hemicellulose-based materials was carried out. Also, their most current developments in a variety of value-added adsorbents, biomedical, energy-related, 3D-printed materials, sensors, food packaging applications were discussed. Additionally, the most recent challenges and prospects of hemicellulose-based materials are emphasized and examined in-depth. It is anticipated that in the near future, persistent scientific efforts will enable the renewable hemicellulose-based products to achieve practical applications.

Recent advances and future perspective on lignocellulose-based materials as adsorbents in diverse water treatment applications

The growing shortage of non-renewable resources and the burden of toxic pollutants in water have gradually become stumbling blocks in the path of sustainable human development. To this end, there has been great interest in finding renewable and environmentally friendly materials to promote environmental sustainability and combat harmful pollutants in wastewater. Of the many options, lignocellulose, as an abundant, biocompatible and renewable material, is the most attractive candidate for water remediation due to the unique physical and chemical properties of its constituents. Herein, we review the latest research advances in lignocellulose-based adsorbents, focusing on lignocellulosic composition, material modification, application of adsorbents. The modification and preparation methods of lignin, cellulose and hemicellulose and their applications in the treatment of diverse contaminated water are systematically and comprehensively presented. Also, the detailed description of the adsorption model, the adsorption mechanism and the adsorbent regeneration technique provides an excellent reference for understanding the underlying adsorption mechanism and the adsorbent recycling. Finally, the challenges and limitations of lignocellulosic adsorbents are evaluated from a practical application perspective, and future developments in the related field are discussed. In summary, this review offers rational insights to develop lignocellulose-based environmentally-friendly reactive materials for the removal of hazardous aquatic contaminants.

Recent insights into mechanism of modified bio-adsorbents for the remediation of environmental pollutants

Rapid industrialization has exacerbated the hazard to health and the environment. Wide spectrums of contaminants pose numerous risks, necessitating their disposal and treatment. There is a need for further remediation methods since pollutant residues cannot be entirely eradicated by traditional treatment techniques. Bio-adsorbents are gaining popularity due to their eco-friendly approach, broad applicability, and improved functional and surface characteristics. Adsorbents that have been modified have improved qualities that aid in their adsorptive nature. Adsorption, ion exchange, chelation, surface precipitation, microbial uptake, physical entrapment, biodegradation, redox reactions, and electrostatic interactions are some of the processes that participate in the removal mechanism of biosorbents. These processes can vary depending on the particular biosorbent and the type of pollutants being targeted. The systematic review focuses on the many modification approaches used to remove environmental contaminants. Different modification or activation strategies can be used depending on the type of bio-adsorbent and pollutant to be remediated. Physical activation procedures such as ultrasonication and pyrolysis are more commonly used to modify bio-adsorbents. Ultrasonication process improves the adsorption efficiency by 15-25%. Acid and alkali modified procedures are the most effective chemical activation strategies for adsorbent modification for pollution removal. Chemical modification increases the removal to around 95-99%. The biological technique involving microbial culture is an emerging field that needs to be investigated further for pollutant removal. A short evaluation of modified adsorbents with multi-pollutant adsorption capability that have been better eliminated throughout the adsorption process has been provided.

Molecular scale behavior of xylan during solvent-controlled extraction and precipitation

Solvent-controlled extraction and precipitation are the most fundamental methods for obtaining hemicellulose from lignocellulosic biomass and purification processes. However, the dissolution and precipitation mechanisms involved have scarcely been mentioned. In this study, the molecular scale behavior of xylan-type hemicellulose during solvent-controlled extraction and precipitation is investigated using molecular dynamics (MD) simulations and density functional theory (DFT) calculations. To bring the model closer to the real extracted xylan, a high degree of polymerization (DP100) of xylan is established, and hemicelluloses with low DP (DP15 and DP50) are also investigated. Four phenomena are explained at the molecular level, including the influence of the polymerization degree and side chain on the solubility of xylan in water, the improvement of the xylan's solubility in NaOH, the precipitation of xylan in ethanol, and the acetyl group preservation of xylan in DMSO. This study contributes to an increased understanding of the dissolution and precipitation mechanisms of hemicellulose and provides a resource for the simulation of high DP hemicellulose, which gives a theoretical basis for the efficient extraction of high-purity hemicellulose as well as economic biorefining.

Unlocking the potential of Dongting Lake-grown Miscanthus lutarioriparius biomass: A comprehensive quality analysis and bioproduct application study

Miscanthus lutarioriparius grown in Dongting Lake has an annual biomass yield potential of 1 million tons. However, with the shutdown of its previous utilization for paper-making, abandoning this huge amount of biomass has caused serious economic, ecological, and social problems. Constructing an industrial cluster to continuously convert biomass into various bioproducts is a win-win measure to address this dilemma. With the increasing confirmation of the importance of biomass quality affecting the conservation process, fully understanding the biomass characteristics of Dongting Lake-grown M. lutarioriparius is crucial for building a scientific industrial cluster. The present work is designed to explore the variation in biomass quality across the entire Dongting Lake area. Results show that the biomass contented with Cd, Mn, Zn, and Cr has significant geographical differences, with a general trend of Southern Dongting Lake-grown biomass having a higher concentration than that from Eastern and Western Dongting Lake areas. Moreover, significant differences are found in terms of biomass ash content, lignin content, and the degree of polymerization of cellulose (DP). The biomass with low ash content is generally from the entire Eastern Dongting Lake area and the northern part of the Western Dongting Lake area. Virtually all Western Dongting Lake-grown biomass has a low lignin content (approximately 18 %). Regarding the spatial variation of DP, Eastern Dongting Lake-grown biomass has a higher DP (average at 585.33) than that in Southern (575.15) and then Western Dongting Lake (529.16). Based on these quality indicators, the biomass production potentials for bioethanol, biochar, and xylo-oligosaccharide were calculated and visualized. Results show that biomass from almost the entire Western and Eastern Dongting Lake area is suitable for bioethanol and xylo-oligosaccharide production, while biomass from the Southern Dongting Lake area for biochar production. These results provide scientific guidance for the future utilization of Dongting Lake-grown M. lutarioriparius biomass.

Structural elucidation of hemicelluloses from oil-tea camellia fruit shell

Oil-tea camellia fruit shell (CFS) is a very abundant waste lignocellulosic resource. The current treatments of CFS, i.e. composting and burning, pose a severe threat on environment. Up to 50 % of the dry mass of CFS is composed of hemicelluloses. However, chemical structures of the hemicelluloses in CFS have not been extensively studied, which limits their high-value utilization. In this study, different types of hemicelluloses were isolated from CFS through alkali fractionation with the assistance of Ba(OH)2 and H3BO3. Xylan, galacto-glucomannan and xyloglucan were found to be the major hemicelluloses in CFS. Through methylation, HSQC and HMBC analyses, we have found that the xylan in CFS is composed of →4)-β-D-Xylp-(1→ and →3,4)-β-D-Xylp-(1→ linked by (1→4)-β glycosidic bond as the main chain; the side chains are α-L-Fucp-(1→, →5)-α-L-Araf-(1→, β-D-Xylp-(1→, α-L-Rhap-(1→ and 4-O-Me-α-D-GlcpA-(1→, connected to the main chain through (1→3) glycosidic bond. The main chain of galacto-glucomannan in CFS consists of →6)-β-D-Glcp-(1→, →4)-β-D-Glcp-(1→, →4,6)-β-D-Glcp-(1→ and →4)-β-D-Manp-(1→; the side chains are β-D-Glcp-(1→, →2)-β-D-Galp-(1→, β-D-Manp-(1→ and →6)-β-D-Galp-(1→ connected to the main chain through (1→6) glycosidic bonds. Moreover, galactose residues are connected by α-L-Fucp-(1→. The main chain of xyloglucan is composed of →4)-β-D-Glcp-(1→, →4,6)-β-D-Glcp-(1→ and →6)-β-D-Glcp-(1→; the side groups, i.e. β-D-Xylp-(1→ and →4)-β-D-Xylp-(1→, are connected to the main chain by (1→6) glycosidic bond; →2)-β-D-Galp-(1→ and α-L-Fucp-(1→ can also connect to →4)-β-D-Xylp-(1→ forming di- or trisaccharide side chains.

Lignocellulosic Bionanomaterials for Biosensor Applications

The rapid population growth, increasing global energy demand, climate change, and excessive use of fossil fuels have adversely affected environmental management and sustainability. Furthermore, the requirements for a safer ecology and environment have necessitated the use of renewable materials, thereby solving the problem of sustainability of resources. In this perspective, lignocellulosic biomass is an attractive natural resource because of its abundance, renewability, recyclability, and low cost. The ever-increasing developments in nanotechnology have opened up new vistas in sensor fabrication such as biosensor design for electronics, communication, automobile, optical products, packaging, textile, biomedical, and tissue engineering. Due to their outstanding properties such as biodegradability, biocompatibility, non-toxicity, improved electrical and thermal conductivity, high physical and mechanical properties, high surface area and catalytic activity, lignocellulosic bionanomaterials including nanocellulose and nanolignin emerge as very promising raw materials to be used in the development of high-impact biosensors. In this article, the use of lignocellulosic bionanomaterials in biosensor applications is reviewed and major challenges and opportunities are identified.

Evaluation of Acemannan in Different Commercial Beverages Containing Aloe Vera (Aloe barbadensis Miller) Gel

Aloe vera (Aloe barbadensis Miller) gel is a frequently used ingredient in many food pro-ducts, particularly beverages, due to its reported health benefits. Studies have identified acemannan, a polysaccharide rich in mannose units which are partially or fully acetylated, as the primary bioactive compound in Aloe vera gel. The acemannan content and its degree of acetylation (DA) were measured in 15 different commercial beverages containing Aloe vera at varying concentrations (from 30% to 99.8%) as listed on the label. Other biopolymers such as pectins, hemicelluloses, and cellulose were also evaluated. Flavoured beverages (seven samples labelled as containing from 30% to 77% Aloe vera) presented low levels of acemannan (<30 mg/100 g of fresh sample) and were fully deacetylated in most cases. These samples had high levels of other polymers such as pectins, hemicelluloses, and cellulose, likely due to the addition of fruit juices for flavour. Unflavoured beverages (eight samples, with Aloe vera concentrations above 99% according to their labels) had variable levels of acemannan, with only three containing more than 160 mg/100 g of fresh sample. In fact, four samples had less than 35 mg acemannan/100 g of fresh sample. DA levels in all but one sample were lower than 35%, possibly due to processing techniques such as pasteurization causing degradation and deacetylation of the acemannan polymer. Legislation regarding Aloe vera products is limited, and manufacturers are not required to disclose the presence or quality of bioactive compounds in their products, leaving consumers uncertain about the true properties of the products they purchase.

Pretreatment of poplar with eco-friendly levulinic acid to achieve efficient utilization of biomass

Organic acid pretreatment is an effective method for green separation of lignocellulosic biomass. However, repolymerization of lignin seriously affects the dissolution of hemicellulose and the conversion of cellulose during organic acid pretreatment. Therefore, a new organic acid pretreatment, levulinic acid (Lev) pretreatment, was studied for the deconstruction of lignocellulosic biomass without adding additional additives. The preferred separation of hemicellulose was realized at Lev concentration 7.0%, temperature 170 °C, and time 100 min. The separation of hemicellulose increased from 58.38% to 82.05% compared with acetic acid pretreatment. It was found that the repolymerization of lignin was effectively inhibited in the efficient separation of hemicellulose. This was attributed to the fact that γ-valerolactone (GVL) is a good green scavenger of lignin fragments. The lignin fragments in the hydrolysate were effectively dissolved. The results provided theoretical support for creating green and efficient organic acid pretreatment and effectively inhibiting lignin repolymerization.

Biobased Nanomaterials─The Role of Interfacial Interactions for Advanced Materials

This review presents recent advances regarding biomass-based nanomaterials, focusing on their surface interactions. Plant biomass-based nanoparticles, like nanocellulose and lignin from industry side streams, hold great potential for the development of lightweight, functional, biodegradable, or recyclable material solutions for a sustainable circular bioeconomy. However, to obtain optimal properties of the nanoparticles and materials made thereof, it is crucial to control the interactions both during particle production and in applications. Herein we focus on the current understanding of these interactions. Solvent interactions during particle formation and production, as well as interactions with water, polymers, cells and other components in applications, are addressed. We concentrate on cellulose and lignin nanomaterials and their combination. We demonstrate how the surface chemistry of the nanomaterials affects these interactions and how excellent performance is only achieved when the interactions are controlled. We furthermore introduce suitable methods for probing interactions with nanomaterials, describe their advantages and challenges, and introduce some less commonly used methods and discuss their possible applications to gain a deeper understanding of the interfacial chemistry of biobased nanomaterials. Finally, some gaps in current understanding and interesting emerging research lines are identified.

Advances in extraction, purification, structural characteristics and biological activities of hemicelluloses: A review

Hemicelluloses, a major component of plant cell walls, are a non-cellulosic heteropolysaccharide composed of several distinct sugars that is second in abundance to cellulose, which are one of the most abundant and cheapest renewable resources on earth. Hemicelluloses structure is complex and its chemical structure varies greatly among the different plant species. In addition to its wide use in production of feed and other chemical materials, hemicelluloses are known for its remarkable biological activities that remain largely underutilised to date. Therefore, comprehensive investigations of hemicelluloses structural and biological properties would be helpful for achieving rational utilisation and high-value conversion of this underutilised substance into agents with enhanced health benefits for incorporation in drugs and health foods. In this review, details of diverse research initiatives that have enhanced our understanding of hemicelluloses properties are summarised, including hemicelluloses sources, extraction and purification methods, structural characteristics and biological activities. Furthermore, hemicelluloses structure-activity relationships and new directions for future hemicelluloses research studies are discussed.

Hemicellulose-based hydrogels for advanced applications

Hemicellulose-based hydrogels are three-dimensional networked hydrophilic polymer with high water retention, good biocompatibility, and mechanical properties, which have attracted much attention in the field of soft materials. Herein, recent advances and developments in hemicellulose-based hydrogels were reviewed. The preparation method, formation mechanism and properties of hemicellulose-based hydrogels were introduced from the aspects of chemical cross-linking and physical cross-linking. The differences of different initiation systems such as light, enzymes, microwave radiation, and glow discharge electrolytic plasma were summarized. The advanced applications and developments of hemicellulose-based hydrogels in the fields of controlled drug release, wound dressings, high-efficiency adsorption, and sensors were summarized. Finally, the challenges faced in the field of hemicellulose-based hydrogels were summarized and prospected.

Eco-friendly and efficient modification of native hemicelluloses via click reactions

An atom-economic strategy is proposed to valorise the byproducts from an invasive bamboo with improved thermal stability for potential use in composites.

In Vitro Assessment of the Prebiotic Potential of Xylooligosaccharides from Barley Straw

Barley straw was subjected to hydrothermal pretreatment (steam explosion) processing to evaluate its potential as a raw material to produce xylooligosaccharides (XOS) suitable for use as a prebiotic. The steam explosion pretreatment generated a liquid fraction containing solubilised hemicellulose. This fraction was purified using gel permeation chromatography to obtain a fraction rich in XOS DP2-DP6. The sample was characterised through analytical techniques such as HPAEC-PAD, FTIR and MALDI-TOF-MS. The prebiotic activity was evaluated using in vitro fermentation in human faecal cultures through the quantification of short-chain fatty acid (SCFA) and lactate production, the evolution of the pH and the consumption of carbon sources. The total SCFA production at the end of fermentation (30 h) was 90.1 mM. Positive significant differences between the amount of XOS from barley straw and fructooligosaccharides after incubation were observed.

Synthesis of Xylan-Click-Quaternized Chitosan via Click Chemistry and Its Application in the Preparation of Nanometal Materials

For the high-valued utilization of hemicelluloses and for realizing the controllable synthesis of NPs, this paper’s aim is to combine xylan, chitosan and nanometal materials at the same time. In this research study, firstly, propargyl xylan was synthesized via nucleophilic substitution reaction between xylan and propargyl bromide in NaOH solution. On the other hand, a tosyl group was introduced onto the 6th position of synthesized quaternized chitosan (QCS), and the azide group replaced the tosyl group to obtain 6-amido-QCS (QCS-N3). The synthesis conditions of the above reactions were optimized. Subsequently, the novel xylan-click-QCS polymer was obtained via click reaction between terminal alkyne groups on the xylan chains and azide groups on QCS. Then, AgNPs and AuNPs were synthesized by adopting the xylan-click-QCS polymer as the reducing and stabilizing agent, and the reaction conditions were optimized to obtain well-dispersed and highly stable nanoparticles. There were two kinds of Ag nanomaterials, with diameters of 10~20 nm and 2~5 nm, respectively, indicating the formation of Ag nanoclusters, except for Ag nanoparticles, in this reaction. The diameter of the synthesized AuNPs was 20~30 nm, which possessed a more uniform size distribution. The Ag nanoclusters with a smaller size (2~5 nm) could inhibit MCF-7 cell proliferation effectively, indicating their application potential in cancer therapy. The study gives a new approach to the high-value utilization of biopolymers.