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Hemicellulose is an important component of plant cell walls, which is mainly used in biofuels and bioproducts. The hemicellulose extracted from different plant sources and plant locations has different microstructure and molecule. Wheat straw is an important biomass raw material for the extraction of hemicellulose. The aims of this review are to summary the recent developments and various applications of hemicellulose from wheat straw. The microstructure and molecule of hemicellulose extracted by different methods are comparably discussed. The hemicellulose-based derivatives and composites are also reviewed. Special attention was paid to the applications of hemicellulose such as biofuel production, packaging field, and adsorbent. The problems and developing direction were given based on our knowledge. We expect that this review will put forward to the development and high-value applications of hemicellulose from wheat straw.

MXenes are a new type of 2D material, featuring numerous favorable properties, such as excellent flexibility, hydrophilicity, abundant functional groups, and high conductivity. Currently, MXene is a hot topic in the field of membrane separation processes. This timely review presents the recent progress in MXene-based membrane in terms of structural engineering and versatile applications. First, the preparation methods for MXene nanosheets and the fabrication technologies for MXene-based membranes are categorized. Then, the separation-based applications of MXene membranes, including gas separation, water treatment, organic solvent purification, nanofluidic ion transport, and osmotic energy conversion, are summarized. Finally, the bottlenecks that limit the application of MXenebased membranes are outlined, and future research prospects are discussed.

Biosorption is an effective method to remove heavy metals from wastewater. In this work, the biosorption of Cd(II) onto Hydrilla verticillata was examined in aqueous solution with parameters of initial pH, adsorbent dosage, contact time, initial Cd(II) concentration, temperature, and co-existing ion. Linear Langmuir and Freundlich models were applied to describe the equilibrium isotherms, and both of the two models were fitted well. The monolayer adsorption capacity of Cd(II) was found to be 50 mg/g at pH 6 and 20°C. Dubinin-Radushkevich isotherm model was also applied to the equilibrium data. The mean free energy of adsorption (11.18 kJ/mol) indicated that the adsorption of Cd(II) onto H. verticillata might be carried out via chemical ion-exchange mechanism. Thermodynamic parameters, including free energy (DG 0 ), enthalpy (DH 0 ), and entropy (DS 0 ) of adsorption, were also calculated. These results showed that the biosorption of Cd(II) onto H. verticillata was a feasible, spontaneous, and exothermic process in nature. Desorption experiments indicated that 0.01 mol/L EDTA and HNO 3 were efficient desorbents for the recovery of Cd(II) from biomass. IR spectrum analysis suggested that amido, hydroxyl, C=O and C-O could combine strongly with Cd(II). EDX spectrum analysis suggested that an ion exchange mechanism might be involved.

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To confirm the prospects for application of pre-corrected pH hydrothermal pretreatment in biorefineries, the effects of pH on the dissolution and degradation efficiency of carbohydrates were studied. The species composition of the hydrolysate was analyzed using high efficiency anion exchange chromatography and UV spectroscopy. The result showed that the greatest balance between the residual solid and total dissolved solids was obtained at pH 4 and 170 • C. Maximum recovery rates of cellulose and lignin were as expected, whereas hemicellulose had the least recovery rate. The hemicellulose extraction rate was 42.19%, and the oligomer form accounted for 93.39% of the product. The physicochemical properties of bamboo with or without pretreatment was characterized. Compared with the traditional hydrothermal pretreatment, the new pretreatment bamboo has higher fiber crystallinity and thermal stability. In the pretreatment process, the fracture of β-aryl ether bond was inhibited and the structural dissociation of lignin was reduced. The physicochemical properties of bamboo was protected while the hemicellulose was extracted efficiently. It provides theoretical support for the efficient utilization of all components of woody biomass.Polymers 2020, 12, 612 2 of 16 environmentally benign process that has been widely used for lignocellulose biomass pretreatment [15]. At present, the research on hydrothermal pretreatment focuses not only on wood materials, but also on bamboo and other non-wood materials [16,17]. The hemicellulose of bamboo was extracted in large quantities during the pretreatment, which effectively promoted the enzymatic hydrolysis efficiency [18]. However, during the hydrothermal pretreatment of bamboo, the degradation of cellulose increased with the dissolution of hemicellulose [17]. Many factors considerably influence the hydrothermal pretreatment of biomass, such as the physical properties of the biomass and the physical and chemical properties [19]. Other factors include the type of reactor and the catalyst. The hydroxyaldehyde condensation reaction can be easily achieved under alkaline conditions [20,21]. Acidic conditions were found to be suitable for dehydration [22]. Sulfuric acid and sodium hydroxide have been used to change the acid-base environment of the reaction. By adjusting the pH, the reaction direction can affect the direction to effective products [23]. High value utilization of woody biomass was promoted by hydrothermal pretreatment. For example, the separation and purification of cellulose were enhanced. The nanocellulose was prepared by oxidation of cellulose [24,25]. The application of nanocomposites was promoted by surface modification/surfactant polymerization of nanocellulose [26,27].A novel, pre-corrected pH hydrothermal pretreatment was performed to integrate pH control without additional steps or equipment, resulting in the best balance between the residual solid and dissolved solid [3]. A buffer system was established by pre-correcting the pH value of the extraction solution. It...

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