The Hy-MASS concept : Hydrothermal microwave assisted selective scissoring of cellulose for: In situ production of (meso)porous nanocellulose fibrils and crystals

The hydrothermal microwave-assisted selective scissoring (Hy-MASS) of depectinated orange peel residues (OPR), produced via conventional acid hydrolysis and acid-free microwave processing, to yield (meso)porous nanocellulose fibrils and crystals simultaneously in the absence of additional auxiliary reagents and/or mechanical treatment is reported. In the stepwise microwave hydrothermal treatment (MHT) of OPR from 120 °C-200 °C at 20 °C intervals, release of residual pectins and hemicelluloses is observed up to 180 °C producing nanocellulose fibrils (3-15 × 500-2000 nm). Beyond 180 °C, selective leaching/hydrolysis of amorphous regions occur to yield nanocellulose crystals (200-400 × 40-50 nm) and crystallites (5-15 × 40-50 nm). This selective, step-wise scissoring process is termed Hy-MASS Concept. Structure, morphology and properties of (meso)porous nanocellulose are strongly influenced by pectin extraction methodology employed. With acid depectinated OPR, deconstruction of the lignocellulosic matrix via microwave is hastened by approx. 20 °C with respect to acid-free microwave depectinated OPR. Td of acid depectinated nanocelluloses (CMC) is ca. 350 °C compared to microwave depectinated nanocelluloses (MMC, Td, varies 342-361 °C). Nanocellulose produced via microwave pre-treatment is (meso)porous: BJH pore size 5-35 nm; BET surface area, 1.5-107 m2 g-1, and; BJH pore volume, 0.01-0.27 cm3 g-1, when compared to acid pre-treated counterparts. The crystallinity index of CMC and MMC increases in two stages, 120-140 °C (ca. 8%) and at 180-200 °C (5-9%). XRD revealed presence of calciuim salts, most likely calcium oxalate. The hydration capacities of nanocelluloses (12-23 g water per g sample) are much higher than their precursors or literature citrus nanocellulose

A novel molybdenum oxide-Starbon catalyst for wastewater remediation

The exploration of novel media for environmental remediation, in particular wastewater treatment, is a global imperative. Herein, the in situ green synthesis, characterisation and application of a novel Starbon™ composite comprising molybdenum oxide nanoparticles are reported. Starbons™ are carbonaceous mesoporous materials derived from starch with applications ranging from chromatography to gas capture. The molybdenum (Mo) loading, evidenced by inductively coupled plasma-mass spectrometry (ICP-MS), was 179.337 mg g-1, and the molybdenum oxide nanoparticles were observed via transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The Mo-containing composite was an efficient catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of sodium borohydride, NaBH4 (k = 11.2 × 10-2 min-1). The Mo-composite showed superior 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical quenching activity with a low inhibitory concentration [IC50 = 1.006 mg ml-1] and ferric reducing power compared with other green synthesised composites and nanoparticles. The novel Mo-containing Starbon™ composite has real time applications in water treatment such as in catalysis, adsorption and filtration

Acid-free microwave-assisted hydrothermal extraction of pectin and porous cellulose from mango peel waste-towards a zero waste mango biorefinery : Towards a Zero Waste Mango Biorefinery

Mango is the second most consumed tropical fruit after banana and the by-products of mango processing (peel, kernel and seed) roughly comprise 35-60% of the total fruit weight, thus representing a potentially high volume resource of exploitable biobased chemicals and materials. Herein, conversion and characterisation of waste mango peels from three different cultivars (Alphonso, Honey and Tommy Atkins) into pectin and porous cellulose using low temperature microwave-assisted acid-free hydrolytic conditions is reported. Microwave-assisted acid-free extraction yielded up to 11.63% (dry weight basis) of pectin which was characterised by IR, NMR (both solution and solid phase) and TGA which showed close similarity to commercial (acid extracted) pectin. The degree of esterification of pectin was determined by 13C NMR (75.6-86.2%) and titrimetry (79.3-87.7%) and the pectin showed excellent gelling ability. The molecular weight as determined by GPC was in the range 14130 (Honey)-25540 (Tommy Atkins). Porosity measurements on the depectinated residue, i.e., residual cellulosic matter showed mesoporous characteristics: average pore diameter, 9.3 nm (Alphonso)-10.5 nm (Honey), however with poor surface area 16.3 m2 g-1 (Honey)-26.0 m2 g-1. Interestingly, a second microwave hydrothermal treatment on these residues retained mesoporosity whilst significantly increasing surface area (88.8 m2 g-1 (Honey)-124.0 m2 g-1 (Alphonso)) and pore volume by approximately six-fold. This is the first detailed combined study of microwave-assisted extraction to yield pectin and mesoporous cellulose towards a potential zero waste mango biorefinery

Exploration of Cucumber Waste as a Potential Biorefinery Feedstock

The exploration of cucumber waste as a potential biorefinery feedstock is reported. Initially, extractives (essential oils) were isolated from cucumber waste via vacuum microwave hydro-distillation (VMHD). The yield and quality of the extractive were compared with respect to traditional hydro-distillation (HD). The essential oils were obtained over a range of microwave power (500, 750, 1000 W) and vacuum pressures (100, 200, 300 mbar). The highest quality (0.49 wt %) was obtained at a microwave irradiation power of 500 W and a vacuum of 300 mbar. VMHD is much quicker and more energy-efficient than HD. Within the context of a zero-waste biorefinery, the extractive-free residues were the solid residues from two different extraction methods were compared and characterized by ATR-IR, 13C solid-state NMR spectroscopy, SEM, TGA, and CHN elemental analysis. The resultant residues are cellulosic-rich, and no significant changes were observed with VMHD and HD treatment. The results indicated that the utilization of these residues can provide an efficient, inexpensive, and environment-friendly platform for the production of cellulosic materials

A New Step Forward Nonseasonal 5G Biorefineries : Microwave-Assisted, Synergistic, Co-Depolymerization of Wheat Straw (2G Biomass) and Laminaria saccharina (3G Biomass)

This investigation explores the microwave-assisted, synergistic co-depolymerization of wheat straw (2G biomass) and Laminaria saccharina (3G biomass) as a novel strategy for the production of sugar-rich aqueous carriers. The effects of the feedstock (each material alone and all the possible binary mixtures) were carefully analyzed over a wide range of reaction temperatures and times. The optimization of the process revealed that 19 wt % of wheat straw and 46 wt % of L. saccharina could individually be converted into an aqueous, high-purity (85-95 C-wt %), sugar-rich solution at 190 °C using reaction times of 18 and 35 min, respectively. The reactivity of wheat straw can be synergistically increased by co-feeding this material a relative amount of seaweed varying between 36 and 57 wt % with respect to the total biomass content at 215 °C for 40 min. This allowed the transformation of 30 wt % of the feedstock mixture into a sugar-rich (90 C-wt %) aqueous solution. The higher reactivity of seaweed than that of wheat straw, as well as the synergistic effects that the former exerted on the depolymerization of the latter, was accounted for by the formation of "a pool of active catalytic species". The mechanism involved an "in situ"metal-biomass, microwave-promoted catalysis with marginal mass transfer limitations followed by metal leaching, leading to a greater spread of the reactions occurring in the liquid phase. This resulted in the formation of new "in situ catalytic species", i.e., carboxylic acids, which acted as homogeneous catalysts and ended up being transformed to gases so that they did not affect sugar purity. Therefore, this novel co-valorization strategy might represent a step-change for the development of novel "nonseasonal, nonfeedstock-dependent"5G biorefineries and can help to render the entire biorefinery for 2G and 3G biomasses more logistically efficient and economically competitive

Tuning the selectivity of natural oils and fatty acids/esters deoxygenation to biofuels and fatty alcohols : A review

The chemical transformation of natural oils provides alternatives to limited fossil fuels and produces compounds with added value for the chemical industries. The selective deoxygenation of natural oils to diesel-ranged hydrocarbons, bio-jet fuels, or fatty alcohols with controllable selectivity is especially attractive in natural oil feedstock biorefineries. This review presents recent progress in catalytic deoxygenation of natural oils or related model compounds (e.g., fatty acids) to renewable liquid fuels (green diesel and bio-jet fuels) and valuable fatty alcohols (unsaturated and saturated fatty alcohols). Besides, it discusses and compares the existing and potential strategies to control the product selectivity over heterogeneous catalysts. Most research conducted and reviewed has only addressed the production of one category; therefore, a new integrative vision exploring how to direct the process toward fuel and/or chemicals is urgently needed. Thus, work conducted to date addressing the development of new catalysts and studying the influence of the reaction parameters (e.g., temperature, time and hydrogen pressure) is summarized and critically discussed from a green and sustainable perspective using efficiency indicators (e.g., yields, selectivity, turnover frequencies and catalysts lifetime). Special attention has been given to the chemical transformations occurring to identify key descriptors to tune the selectivity toward target products by manipulating the reaction conditions and the structures of the catalysts. Finally, the challenges and future research goals to develop novel and holistic natural oil biorefineries are proposed. As a result, this critical review provides the readership with appropriate information to selectively control the transformation of natural oils into either biofuels and/or value-added chemicals. This new flexible vision can help pave the wave to suit the present and future market needs

Defibrillated celluloses via dual twin-screw extrusion and microwave hydrothermal treatment (MHT) of spent pea biomass

The defibrillation of lignocellulosic matter from pea waste using a dual approach of twin-screw extrusion and microwave hydrothermal treatment (MHT) in the presence of water alone from 120 to 200 °C is reported. Gradual "scissoring" of biomass macrofibers to microfibrils was observed alluding to the hydrothermal microwave-assisted selective scissoring (Hy-MASS) concept. The morphology and properties of two types of MFC: PEA (nonextruded) and EPEA (extruded) were compared. The EPEA samples gave a higher crystallinity index and thermal stability, reduced lignin and hemicellulose content, narrower fibril width, better water holding capacity slightly, and higher surface area compared with their nonextruded counterparts (PEA). Twin screw extrusion as a pretreatment method followed by MHT represents a potential way to produce microfibrillated cellulose with improved physical performance from complex biomass sources

Unforeseen crystal forms of the natural osmolyte floridoside

Floridoside (2-α-O-D-galactopyranosyl glycerol) is a glycerol glycoside that is biosynthesised by most species of red algae and has been implicated as an intracellular regulator of various homeostatic functions. Here, we report the identification of two unforeseen crystal forms of the ubiquitous natural osmolyte floridoside including a seemingly unheralded second anhydrous conformational polymorph and the unambiguous description of an elusive monohydrated variant. By employing a variety of thermal and spectroscopic techniques, we begin to explore both their macro and molecular physicochemical properties, which are notably different to that of the previously reported polymorph. This work advances the characterisation of this important natural biomolecule which could aid in facilitating optimised utilisation across a variety of anthropocentric applications and improve comprehension of its role in-vivo as a preeminent compatible solute

Deep Eutectic Solvents Based on Natural Ascorbic Acid Analogues and Choline Chloride

Deep eutectic solvents (DES) are one of the most promising green technologies to emerge in recent years given their combination of environmentally friendly credentials and useful functionalities. Considering the continued search for new DES -- especially those that exemplify the aforementioned characteristics, we report the preparation of DES based on natural analogues of L-ascorbic acid for the first time. The onset of eutectic melting occurred at temperatures far below the melting point of the individual components and resulted in the generation of glass forming fluids with glass transition temperatures, viscosities and flow behavior that are comparable to similar systems. This work expands the current array of DES that can be produced using naturally occurring components, which given their potential to be bio-derived, interesting physicochemical properties (e.g. propensity to supercool and vitrify) and apparent antibacterial nature, may provide utility within a range of applications

From unavoidable food waste to advanced biomaterials : microfibrilated lignocellulose production by microwave-assisted hydrothermal treatment of cassava peel and almond hull

Lignocellulose based nanomaterials are emerging green biosolids commonly obtained from wood pulp. Alternative feedstocks, such as as unavoidable food waste, are interesting resources for nano/microfibers. This research reports the production and characterization of microfibrillated lignocellulose (MFLC) from cassava peel (CP) and almond hull (AH) via acid-free microwave-assisted hydrothermal treatment (MHT) at different temperatures (120–220 °C). During processing, the structural changes were tracked by ATR-IR, TGA, XRD, 13C CPMAS NMR, zeta potential, HPLC, elemental analysis (CHN; carbon, hydrogen and nitrogen), TEM and SEM analyses. The microwave processing temperature and nature of feedstock exerted a significant influence on the yields and properties of the MFLCs produced. The MFLC yields from CP and AH shifted by 15–49% and 31–73%, respectively. Increasing the MHT temperature substantially affected the crystallinity index (13–66% for CP and 36–62% for AH) and thermal stability (300–374 °C for CP and 300–364 °C for AH) of the MFLCs produced. This suggested that the MFLC from CP is more fragile and brittle than that produced from AH. These phenomena influenced the gelation capabilities of the fibers. AH MFLC pretreated with ethanol at low temperature gave better film-forming capabilities, while untreated and heptane pretreated materials formed stable hydrogels at solid concentration (2% w/v). At high processing temperatures, the microfibrils were separated into elementary fibers, regardless of pretreatment or feedstock type. Given these data, this work demonstrates that the acid-free MHT processing of CP and AH is a facile method for producing MFLC with potential applications, including adsorption, packaging and the production of nanocomposites and personal care rheology modifiers. Graphic abstract: [Figure not available: see fulltext.