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

Potential Utilization of Unavoidable Food Supply Chain Wastes – Valorisation of Pea Vine Wastes

Combating food waste is a vital 21st century global challenge befitting of green and sustainable chemistry. Prevention is the first and foremost route for reduction of food waste, but inevitably, there are unavoidable food losses as a result of primary and secondary processing that represents an interesting green and sustainable chemistry valorization opportunity. Herein, pea vine waste (Pisum sativum) as an unavoidable food supply chain waste is explored as the source for (bio)­renewable chemicals and materials and as a potential bioenergy source. Through a cascade approach simulating a potential biorefinery, pea vine waste was subjected to pseudosubcritical water extraction as a green extraction methodology technique to extract potential platform molecules: 5-hydroxy furfural (HMF); ethanoic acid; sugars (levoglucosenone, rhamnose, xylose, fructose, glucose and sucrose); and a precipitated biopolymer showing pectinaceous and starch-like characteristics as evidenced by infrared spectroscopy, solid-state ¹³C NMR, and thermogravimetric analysis. The postextraction residues of pea vine waste were further subjected to microwave pyrolysis to produce a bio-oil and a biochar. The bio-oil is rich in phenolic compounds while the biochar has a gross calorific value of 26.6 MJ kg^–1 and thus may be used as a potential source of bioenergy. While peas alone have been explored previously, the work within represents the first study of valorization of pea vine wastes, a real as-received industrial problematic waste source, using a cascade approach of pseudo-sub-critical water and microwave pyrolysis simulating a potential biorefinery

Production of Hydrogels from Microwave-Assisted Hydrothermal Fractionation of Blackcurrant Pomace

The exploitation of unavoidable food supply chain wastes resulting from primary and secondary processing for chemicals, materials, and bioenergy is an important concept in the drive towards circular-based, resource-efficient biorefineries rather than petroleum refineries. The potential production of hydrogels (materials) from unavoidable food supply chain wastes, which are naturally rich in biopolymers such as cellulose, hemicellulose, pectin, and lignin, represents an interesting opportunity. However, these intertwined and interconnected biopolymers require separation and deconstruction prior to any useful application. Thus, this study aims to explore the formation of hydrogels from defibrillated celluloses (MW-DFCs) produced via acid-free stepwise microwave hydrothermal processing of blackcurrant pomace residues. Initially, pectin was removed from blackcurrant pomace residues (MW, 100–160 ◦C), and the resultant depectinated residues were reprocessed at 160 ◦C. The pectin yield increased from 2.36 wt.% (MW, 100 ◦C) to 3.07 wt.% (MW, 140 ◦C) and then decreased to 2.05 wt.% (MW, 160 ◦C). The isolated pectins were characterized by attenuated total reflectance infrared spectroscopy (ATR-IR), thermogravimetric analysis (TGA), and 13C NMR (D2O). The cellulosic-rich residues were reprocessed (MW, 160 ◦C) and further characterized by ATR-IR, TGA, and Klason lignin analysis. All the MW-DFCs contained significant lignin content, which prevented hydrogel formation. However, subsequent bleaching (H2O2/OH−) afforded off-white samples with improved gelling ability at the concentration of 5% w/v. Confocal laser microscopy (CLSM) revealed the removal of lignin and a more pronounced cellulosic-rich material. In conclusion, the microwave-assisted defibrillation of blackcurrant pomace, an exploitable unavoidable food supply chain waste, affords cellulosic-rich materials with the propensity to form hydrogels which may serve useful applications when put back into food products, pharmaceuticals, cosmetics, and home and personal care products

Microwave-Assisted Defibrillation of Microalgae

The first production of defibrillated celluloses from microalgal biomass using acid-free, TEMPO-free and bleach-free hydrothermal microwave processing is reported. Two routes were explored: i. direct microwave process of native microalgae (“standard”), and ii. scCO2 pre-treatment followed by microwave processing. ScCO2 was investigated as it is commonly used to extract lipids and generates considerable quantities of spent algal biomass. Defibrillation was evidenced in both cases to afford cellulosic strands, which progressively decreased in their width and length as the microwave processing temperature increased from 160 °C to 220 °C. Lower temperatures revealed aspect ratios similar to microfibrillated cellulose whilst at the highest temperature (220 °C), a mixture of microfibrillated cellulose and nanocrystals were evidenced. XRD studies showed similar patterns to cellulose I but also some unresolved peaks. The crystallinity index (CrI), determined by XRD, increased with increasing microwave processing temperature. The water holding capacity (WHC) of all materials was approximately 4.5 g H2O/g sample. The materials were able to form partially stable hydrogels, but only with those processed above 200 °C and at a concentration of 3 wt% in water. This unique work provides a new set of materials with potential applications in the packaging, food, pharmaceutical and cosmetic industries

Superior Mesoporosity of Lipid Free Spent Coffee Grounds Residues

As part of the biorefinery concept for spent coffee grounds (SCG), production of activated carbon (AC) was investigated from the degreased coffee grounds (DCG) left behind after oil extraction (primarily for biodiesel). The oils were extracted via conventional solvent extraction with GC/GC-MS confirming the oil was comparable to oils produced industrially. More significantly, analysis showed the DCG AC to have a 4-fold increase in mesoporosity than the SCG AC with mesopore volumes of 0.6 and 0.15 cm3 g-1 respectively. Adsorption trials showed a ten-fold increase in capacity for Au(III) from 8.7 to 88.6 mg/g with subsequent experiments confirming that DCG AC displayed standard behavior for mesoporous materials of increasing adsorption capacity with decreasing pH. This raises the potential for valorization of SCG into a functional material for water remediation without the need for templating agents or expansion pre-treatments with the added bonus of an additional material being produced simultaneously

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

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

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