Search

In the recent decade, carbon dots have drawn immense attention and prompted intense investigation. The latest form of nanocarbon, the carbon nanodot, is attracting intensive research efforts, similar to its earlier analogues, namely, fullerene, carbon nanotube, and graphene. One outstanding feature that distinguishes carbon nanodots from other known forms of carbon materials is its water solubility owing to extensive surface functionalization (the presence of polar surface functional groups). These carbonaceous quantum dots, or carbon nanodots, have several advantages over traditional semiconductor-based quantum dots. They possess outstanding photoluminescence, fluorescence, biocompatibility, biosensing and bioimaging, photostability, feedstock sustainability, extensive surface functionalization and bio-conjugation, excellent colloidal stability, eco-friendly synthesis (from organic matter such as glucose, coffee, tea, and grass to biomass waste-derived sources), low toxicity, and cost-effectiveness. Recent advances in the synthesis and characterization of carbon dots have been received and new insight is provided. Presently known applications of carbon dots in the fields of bioimaging, drug delivery, sensing, and diagnosis were highlighted and future applications of these astounding materials are speculated.

Biodiesel is a renewable and environmentally friendly alternative to fossil fuels. Despite nearly 3 decades of research in the field of biodiesel, there remains major obstacles for large-scale prod...

Bioethanol and direct glucose fuel cells pledged clean energy to the world. Cellulose depolymerization for glucose production has been a successful approach in bioethanol production. Heteropoly acids (HPAs) are strong Bronsted solid acid catalysts for biomass hydrolysis. Keggin type HPAs, namely, Silicotungstic acid (HSiW), Phosphotungstic acid (HPW), and Phosphomolybdic acid (HPMo), were used for the hydrolysis of lignocellulosic biomass to glucose. Five different biomass feedstocks, namely, miscanthus, sugarcane leaves, switchgrass, sunflower seeds, and bamboo leaves, were examined for the feasibility of total reducing sugar (TRS) yield through the composition analysis and catalytic biomass hydrolysis. Sunflower seeds contained the maximum holocellulose with 90.6%, and switchgrass contained the least i.e., 77.63%. Among the five biomass tested, switchgrass resulted in the highest TRS (5.77 wt/dry wt. %) with HPMo catalyst at a catalyst to biomass ratio of 30:100 (wt./wt. %), a reaction temperature of 120 °C for 3 h. The reaction parameters for depolymerization were optimized for all three HPAs, and the optimized conditions were 3 h and 120 °C. HPMo showed maximum TRS yield (5.77 wt/dry wt.%) among the three HPAs at 30:100 catalyst to biomass ratio. However, a catalyst to biomass ratio of 20:100 (wt./wt.%) was economical (5.25 wt/dry wt.%) for commercial application.

The use of green and inexpensive organic nitrile (MeCN) as a cyano and cyano-methyl source for organo-complexation, cyanation, and cyanomethylation is reviewed. In recent decade, a lot of developments have been made to realize the possibility of using a green cyanide source (MeCN) for cyanation, and this CN source has been used as, for example, a slow dosage cyanide source that could solve the problem of using metal cyanides (K4[Fe(CN)6], Zn(CN)2, KCN, CuCN, NaCN), which (1) tend to cause rapid deactivation of the catalyst and (2) are notoriously toxic, producing highly toxic HCN gas in reactions. In view of these problems, here we attempted to discuss new catalyst systems to achieve the cyanation of various aromatic hydrocarbons, such as aryl halides, aryl boronic acids, aryl carboxylic acids, indoles, diazoarenes, aryl alkynes, aryl sulfonamides, and directing group substituted arenes, under variety of reaction parameters. Moreover, acetonitrile is used as the carbon pro-nucleophile in C–C bond formation, which involves complications usually associated with the catalyst active mode or its resting state. This review demonstrates a set of innovations for practical usage via direct complexation, cyanation and cyanomethylation methodologies.

Low thermal conductivity is the major obstacle for the wide range utilization of phase change materials (PCMs), especially organic PCMs, for most practical applications in thermal engineering. This study investigates the potential of enhancing the charging and discharging rates of organic PCM (RT44HC) by introducing polyethylene glycol (PEG) and activated carbon macroparticles (ACMPs). Different concentrations of PEG and ACMPs ranging from 0.3 wt% to 2 wt% were tested separately. The optimized concentrations found were used as dual reinforcements to attain the highest possible thermal conductivity. The specimens were tested for a complete charging–discharging cycle using an improvised thermal apparatus. Use of ACMP alone resulted in a minimal reduction in complete charging–discharging time due to the settlement of ACMPs at the bottom after 2–3 heating–cooling cycles. However, the addition of PEG with ACMPs exhibited a reduction in charging–discharging time due to the formation of a stable dispersion. PEG served as a stabilizing agent for ACMPs. The lowest charging–discharging time of 180 min was exhibited by specimens containing 1 wt% PEG and 0.5 wt% ACMPs which is 25% lower compared to bare PCM.

Among various renewable energy sources, namely, biomass, solar, wind, hydrothermal and geothermal, biomass standout as an environmentally benign, sustainable and an immediate substitute to fossil based fuels. This is due to the abundance of the carbon source in the form of cellulose in the biomass. Cellulose is the major chemical constituent of terrestrial biomass (40-50 wt.%, percentage by weight) with the other constituents being hemicellulose and lignin.

Furfural is a versatile biomass-derived platform compound used for the synthesis of several strategic chemicals. The sonochemically synthesized Zn doped CuO nanoparticles (NPs) were used for the production of furfural. The catalytic activity of the Zn doped CuO NPs was examined, as a model, during the dehydration reaction of xylose to furfural. In addition to that, we have also compared the catalytic activity of the Zn doped CuO NP with ZnO NPs, ZnO bulk, CuO NPs, CuO bulk, etc. This nanoscale catalyst (Zn doped CuO NP) has a large surface area, which enhances its catalytic activity and enables it to completely convert the xylose to furfural at 150 °C within 12 h without any trace of by-products, as confirmed by HPLC, 13C NMR and 1H NMR. HPLC analysis demonstrated that the yield of furfural is up to 86 mol %, compared to the 45 mol % obtained with ZnO NPs, ZnO bulk, CuO NPs, CuO bulk, etc. as catalysts.

Levulinic acid (LA) is one of the top twelve chemicals listed by the US Department of Energy that can be derived from biomass. It serves as a building block and platform chemical for producing a variety of chemicals, fuels and materials which are currently produced in fossil based refineries. LA is a key strategic chemical, as fuel grade chemicals and plastic substitutes can be produced by its catalytic conversion. LA derivatisation to various product streams, such as alkyl levulinates via esterification, γ-valerolactone via hydrogenation and N-substituted pyrrolidones via reductive amination and many other transformations of commercial utility are possible owing to the two oxygen functionalities, namely, carbonyl and carboxyl groups, present within the same substrate. Various biomass feedstock, such as agricultural wastes, marine macroalgae, and fresh water microalgae were successfully converted to LA in high yields. Finding a substitute to mineral acid catalysts for the conversion of biomass to LA is a challenge. The use of an ultrasound technique facilitated the production of promising nano-solid acid catalysts including Ga salt of molybophosphoric acid and Ga deposited mordenite zeolite, with optimum amounts of Lewis and Bronsted acidities needed for the conversion of glucose to LA in high yields, being 56 and 59.9 wt.% respectively. Microwave irradiation technology was successfully utilized for the accelerated production of LA (53 wt.%) from glucose in a short duration of 6 min, making use of the unique synergistic catalytic activity of ZnBr2 and HCl.

The advent of microwave technology and its application to transesterification reaction has revolutionized the biodiesel production process. Unambiguously the microwave-activated solid base catalyzed process is recommended for industrial adaptation. Several solid base catalysts were developed among which SrO-based catalyst supported on millimetric silica beads and SrO supported on porous titanium matrix stand out. Sonochemical methods of activation have the potential for acceleration of biodiesel production. However, the use of homogenization reactor outperformed sonication technology for large-scale utility of biodiesel production. Use of activation methods like microfluidic reactor and solar energy for biodiesel production should not be neglected and should be developed on a par with microwave technology. State-of-the-art methods developed for the production of biodiesel using nontraditional methods of activation, namely, microwave and sonication, have been reviewed (especially the recent innovation in the field published during 2018). The role of microwave and sonochemical activation leading to the accelerated production of biodiesel, glucose, and bioethanol from biomass was elucidated. Microwave technology for glucose production through the biomass hydrolysis reaction is as promising as that of biodiesel production pathway from lipid sources. The potential of sonication for the acceleration of the key bioethanol production reactions from biomass, namely, fermentation and simultaneous saccharification and fermentation, was elaborated. Bioethanol production in a solar reactor is particularly rewarding if exploited in industrial units.

Bioethanol is one of the most promising transportation fuels with economic, environmental, and energy benefits. However, currently, the production methodologies and purification technologies of the biofuel industry are not economical. This review demonstrates an economically viable, energy efficient, and sustainable alternative to the state-of-the-art process for bioethanol production from biomass. We have developed a solar-thermal-energy-driven simultaneous saccharification and fermentation (SSF) process for single-step conversion of biomass to bioethanol. In the early stages, aqueous solutions of glucose, starch, or cellulose were fed into a specially designed solar reactor containing instant baker's yeast (Saccharomyces cerevisiae) and the necessary enzymes. The yeast (biocatalyst) was not supplemented by any other nutrient, and it was demonstrated that the same yeast and enzymes could be used for at least two months without any decrease in enzymatic activity. After obtaining very high yields (up to 91% of the theoretical yield) and excellent separation of ethanol from the fermentation broth, the methodology was successfully extended to a continuous-flow single-step conversion of marine algae Ulva rigida to bioethanol (84% of the theoretical yield). Harnessing solar thermal energy for driving the SSF reaction as well as the special design of the solar reactor that facilitates in situ separation of ethanol from the fermentation broth by an evaporation–condensation process make the current method industrially appealing and adoptable for large-scale production. This review explores new avenues for a decentralized power supply based on solar thermal energy. The bioethanol produced in this study was demonstrated as a potential fuel for direct ethanol fuel cells with high current and power density values, and 65% thermodynamic efficiency. In addition, the secondary metabolite glycerol was fully reduced to the value-added product 1,3-propanediol by S. cerevisiae, which is the first example of a fungal strain converting glycerol in situ to 1,3-propanediol. In this review, we aim to discuss the current methodologies and recent developments for bioethanol production from biomass and demonstrate the future aspects of bioethanol production in solar reactors, and strategies to improve process yields as well as the prospects of using a solar reactor to produce other valuable chemicals.

A more facile and more efficient self-healing strategy for carbon fiber/thermoset resin interphase was established based on electrothermal effect of carbon fiber (CF) driving the reversible transformation of covalent bonds. Diels-Alder cycloaddition adduct was introduced into the CF/epoxy (EP) interphase region to endow the interphase with thermoreversible covalent bonds through the oxidative co-polymerization and chemical surface grafting, which was nondestructive but more efficient. The modified carbon fiber was characterized via SEM, AFM, XPS and TGA. The CF/EP interphase temperature range in CF reinforced polymer composites (CFRPs) was adjusted through controlling the electric current applied to CFs according to the thermo-sensitivity of CF. The effect of electrothermal effect on the matrix resin around CFs was measured by micro-FTIR. The interfacial shear strength (IFSS) measurement verified that the electrothermal effect promoted the reversible transformation of the Diels-Alder cycloaddition adducts connecting the modified CFs with matrix resin, resulting in the self-healing behavior of the damaged interphase. This self-healing strategy not only can improve the interfacial adhesion of CFRPs without damages to the CF surface caused by the traditional oxidation modification methods, but also can reduce the possible heating aging and deformation of composites caused by convective thermal repairing methods. This strategy is a more efficient process.

The main goal of this study is to functionalize SrO with carbon dots (C-dots) and to explore the composite as a catalyst for fatty acid methyl esters (FAME) production using Chlorella vulgaris as feedstock. C-dots are synthesized by sonicating polyethylene glycol followed by sonochemical modification of Sr(NO3)2 (precursor for SrO) with C-dots. Sonication facilitates the adhesion of C-dots to the surface of Sr(NO3)2. The resulting material is calcined in an inert environment to form a SrO–C-dot composite. The effect of functionalizing SrO with C-dots on the transesterification of the lipids in the alga with methanol is studied. The optimization of a one-stage process of conversion of the lipid fraction of microalga Chlorella vulgaris into FAME using direct transesterification under microwave irradiation is illustrated. A lipid conversion value of 45.5 wt % is achieved using the SrO–C-dot catalyst after 2.5 min of microwave (MW) irradiation. The catalyst displayed better activity than commercial SrO. Micro...

Efficient catalytic methods for biomass conversion present a challenge for the sustainable production of fuels and chemicals. Ga salt of molydophosphoric acid (GaHPMo) is prepared using a sonochemical irradiation method. Simultaneous formation of GaHPMo and entrapment of polyoxometallate in gallium micro-/nanoparticles (Ga@HPMo) is achieved. The amount of entrapped hetropoly acid in Ga particles is estimated to be ∼3 wt %, as determined from thermogravimetric analysis (TGA) and ultraviolet–visible (UV–vis) analysis. The preparation of GaHPMo is accomplished by subjecting an ethanolic solution of polyoxometallate [molybdophosphoric acid (HPMo)] and molten Ga metal to sonication at 50 °C for 12 min. Physicochemical properties of GaHPMo are studied using X-ray diffraction, TGA, temperature-programmed desorption, differential scanning calorimetry, Fourier transform infrared spectroscopy, UV–vis spectroscopy, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, and energy-d...

Gallium modified zeolite (mordenite), a solid acid catalyst, was prepared using the sonochemical method. The catalyst (Ga@mordenite) was characterized using XRD, SEM, TEM, EDS, FT-IR, DSC TGA, TPD and XPS analysis. Uniform distribution of Ga on the zeolite surface was confirmed from the SEM-EDS analysis. The catalyst was further used for the production of levulinic acid (LA) from carbohydrates (glucose, starch, and cellulose) in a hydrothermal process. Reaction conditions (time, 6 h; temperature, 175 °C) for the optimum yield of LA (59.9 wt. %) were deduced. The reaction products were analyzed qualitatively using 13C NMR and quantified using HPLC analysis. Synergistic effect of the Lewis acid sites of Ga3+ generated in situ and the Bronsted acid sites of mordenite were found to be crucial for the activity of Ga@mordenite for the conversion of glucose to levulinic acid.

Gallium oxide (β-Ga2O3) nanorods were prepared by ultrasonic irradiation of molten gallium in warm water to form α-GaO(OH). This precursor was then subjected to calcination in air at 600 °C for 3 h to form β-Ga2O3, as confirmed by X-ray diffraction (XRD). Field emission scanning electron microscopy (FE-SEM)/high-resolution transmission electron microscopy (HRTEM) micrographs revealed the formation of well-organized nanotubes/nanorods with homogeneous size distribution. The average length of the β-Ga2O3 nanorods was affected by the temperature of the water during sonication, decreasing from 480 to 72 nm with an increase in the temperature from 25 to 50 °C. A sharp decline in the particle size was also observed when the temperature was above 35 °C. The catalytic activity of the β-Ga2O3 nanorods was examined, as a model, during the dehydration reaction of xylose to furfural. Furfural is a versatile biomass-derived platform compound used for the synthesis of several strategic chemicals. This nanoscale catalys...

A microwave assisted feasible process for the production of bioethanol from Ficus religiosa leaves was developed. Under the process conditions (8 min. microwave irradiation, 1 M HCl), 10.1 wt% glucose yield was obtained from the leaves. Microwave based hydrolysis process yielded higher glucose content (10.1 wt%) compared to the conventional hydrothermal process (4.1 wt%). Upon fermentation of the hydrolysate using Baker's yeast, 3 wt% (dry wt. basis) of bioethanol was produced.

Potato starch was chemically hydrolyzed to glucose using silicotungstic acid (H4SiW12O40·nH2O, HSiW) as catalyst under microwave irradiation in a short duration (5 min). Potato starch was completely converted to glucose, levulinic acid and formic acid. The methodology was further used for the conversion of potato peel waste (PPW), a zero value waste to glucose. A glucose yield of 59 wt.% was obtained upon the microwave irradiation (15 min) of PPW. The combined use of solid acid catalyst and microwave irradiation offers a fast and green process for glucose production from starch based waste materials.

Energy sources are necessary for human existence, comfort, and progress. Limited crude petroleum resources and increasing awareness of the environmental impacts of using fossil fuels motivate the search for new energy sources and alternate fuels. Herein, a low cost, fast, and green methodology for the synthesis of a hybrid solid base catalyst, strontium oxide coated millimetric silica beads (SrO@SiO2), is designed for the transesterification of cooking oil into biodiesel in a domestic microwave oven. The cost reduction is due to the effective utilization of the catalyst by the homogeneous dispersion of the active sites on the silica beads and their reusability. The catalyst synthesis process was optimized with respect to the amount of glass beads, microwave irradiation time, calcination time, and calcination temperature. Several methods for synthesizing SrO by minimizing energy consumption were investigated, and an optimized process for designing SrO@SiO2 was developed. The SrO@SiO2 catalyst produced unde...

For bioethanol to be a sustainable transportation fuel, appropriate feedstock needs to be established. The focus of the current work is to evaluate if the microalga Chlorella vulgaris could be the feedstock of choice. Exclusive formation of glucose was observed upon the acid (HCl) hydrolysis of C. vulgaris. Microwave irradiation as well as hydrothermal reaction were employed as heating methods. Under optimal hydrolysis conditions using microwave irradiation (100 °C, 1 M HCl, and 10 min), the glucose yield was 20 ± 3.5 wt % compared to 23 ± 4 wt % under the optimal hydrothermal reaction conditions (120 °C, 1 M HCl, and 60 min). The hydrothermal-based hydrolysis process was further scaled up from a 0.2 g batch to a 2.0 g batch, and the glucose obtained was converted to bioethanol in a fermentation process at 30 °C for 28 h using Saccharomyces cerevisiae. An ethanol yield as high as 13.2 ± 0.5 wt % was obtained from C. vulgaris.

The focus of the present research is to develop energy-efficient, sustainable, and continuous-flow bioethanol production based on solar energy. Solid-state fermentation of glucose was performed in a specially designed solar-energy-driven continuous flow reactor. Aqueous glucose solutions of 10 and 20 wt% were fed into the reactor bed containing baker's yeast (Saccharomyces cerevisiae), resulting in 4.7 and 8.7 wt% ethanol yields, respectively. The bioethanol produced was separated from the yeast bed soon after its formation by an evaporation–condensation process. High ethanol yields (91.2 and 85.5% of the theoretical yield, respectively) indicate the atom-efficiency of the process. No loss in the activity of yeast was observed even after two months of continuous operation of the reactor. The current study demonstrates an energy-efficient methodology for bioethanol production utilizing solar energy. The bioethanol obtained (8.7 wt%, ca. 2 M) was further tested in alkaline-acid direct ethanol fuel cells operated at 303 K, resulting in a power density value of 330 mW cm−2 at a modest open circuit voltage value of 1.65 V (65.5% voltage efficiency).

A selective, green and fast method for the production of glucose from rice (Oryza sativa) straw is demonstrated. Aq. ammonia based pretreatment techniques played a crucial role in the removal of lignin and xylan from rice straw which in-turn accelerated glucan hydrolysis and improved the selectivity of glucose production. The cellulose isolated from rice straw is further hydrolyzed to glucose using a solid acid catalyst (activated carbon supported phosphotungstic acid, ∼40 wt% HPW/AC). Microwave irradiation of cellulose from rice straw for a short duration of 5 min at 100 °C yielded 11.2 wt% glucose relative to 8 wt% glucose produced from a hydrothermal hydrolysis process (3 h, 150 °C) with a substrate to catalyst wt/wt ratio of 1. Thus an effective biomass pretreatment (aq. ammonia–dil. H2SO4) method and an accelerated selective biomass hydrolysis process is developed.

The demand for 1,3-propanediol-based polymers is constantly increasing, necessitating an increase in 1,3-propanediol production. While the processes for the chemical and bacterial synthesis of 1,3-propanediol are well-known, we report for the first time the possibility of glycerol conversion to 1,3-propanediol by a fungal strain. The synthesis of 1,3-propanediol by biological means is extremely lucrative, and to the best of our knowledge, this is the first study focusing on the development of an optimized process for the production of the value-added chemical 1,3-propanediol from what can be considered as industrial waste, glycerol, via fermentation using instant baker's yeast (Saccharomyces cerevisiae). Various glycerol fermentation conditions (aerobic, semi-aerobic, and anaerobic) were tested at different reaction temperatures (25, 30, and 37 °C). Under optimal reaction conditions (anaerobic fermentation at 25 °C), 42.3 wt% 1,3-propanediol yield was achieved with 93.6 wt% glycerol conversion.

A simple analytical method is designed for the detection of micro-molar concentrations of an antibiotic with a β-lactam subunit. The sensor for ampicillin has a limit of detection, LOD, value of 0.165 × 10−4 M and exhibited linearity over a wide range of ampicillin concentrations (6.6–200 ppm). The detection of the antibiotic is based on the in situ generation of carbon nanodots (CNDs) via a hydrothermal reaction between glucose and the antibiotic moiety. The CNDs exhibited characteristic absorption at 340 nm whose intensity is a measure of the initial ampicillin concentration. The CNDs possess peculiar blue emission which is excitation independent. The particle size of CNDs is in the range of 8–40 nm and they are hydrophilic in nature. NMR spectral analysis revealed insights into the carbon nano-structure comprising of an aromatic core with carbonyl type functionalities on its surface. Synthesis of carbon dots from ampicillin in aqueous medium and utilizing the absorption properties as well as the emission properties of the carbon dots generated for the detection of ampicillin make the design and operation of the sensor environmentally friendly and simple.

Renewable and green energy sources are much sought. Bioethanol is an environmentally friendly transportation fuel. Pine cones from Pinus radiata were shown to be a potential feedstock for the production of bioethanol. Alkaline (NaOH) pretreatment was carried out to delignify the lignocellulosic material and generate holocellulose (72 wt. % yield). The pretreated biomass was hydrolysed using HCl as catalyst under microwave irradiation and hydrothermal conditions. Microwave irradiation was found to be better than the hydrothermal process. Microwave irradiation accelerated the hydrolysis of biomass (42 wt. % conversion) with the reaction conditions being 3 M HCl and 5 min of irradiation time. Interestingly, even the xylose, which is the major component of the hydrolyzate was found to be metabolized to ethanol using Baker's yeast (Saccharomyces cerevisiae) under the experimental conditions. 5.7 g of ethanol could be produced from 100 g of raw pine cones.

A solar reactor was designed to perform the conversion of starch to ethanol in a single step. An aqueous starch solution (5 wt %) was fed into the reactor bed charged with Baker's yeast (Saccharomyces cerevisiae) and amylase, resulting in approximately 2.5 wt % ethanol collected daily (ca. 25 mL day(-1) ). A significant amount of ethanol (38 g) was collected over 63 days, corresponding to 84 % of the theoretical yield. The production of ethanol without additional energy input highlights the significance of this new process. The ethanol produced was also demonstrated as a potential fuel for direct ethanol fuel cells. Additionally, the secondary metabolite glycerol was fully reduced to a value-added product 1,3-propanediol, which is the first example of a fungal strain (Baker's yeast) converting glycerol in situ to 1,3-propanediol.

Activated carbon supported silicotungstic acid is used as catalyst for the hydrolysis of starch to glucose. The selectivity of the hydrothermal process for glucose production is demonstrated. Byproducts such as levulinic and formic acids are not formed. Separation of the catalyst is easy, and the catalyst reusability is demonstrated in five consecutive reaction runs. No appreciable loss in activity and selectivity of the catalyst is observed even after 5 consecutive reaction runs. Leaching of the heteropoly acid into the reaction medium is not observed. The yield of glucose (94 wt. %) is close to the theoretical yield (111 wt. %) possible from starch. Thus the glucose production process is atom efficient and green.

Complete conversion of glycogen to glucose is achieved by using H3PW12O40·nH2O (HPW) and H4SiW12O40·nH2O (HSiW) as catalysts for the hydrolysis under optimized hydrothermal conditions (mass fraction of catalyst 2.4%, 373 K and 2 h reaction time). The reusability of the catalyst (HPW) was demonstrated. In addition to carrying out the glycogen hydrolysis in an autoclave, other novel methods such as microwave irradiation and sonication have also been investigated. At higher mass fraction of the heteropoly acids (10.5%), glycogen could be completely converted to glucose under microwave irradiation. Sonication of an aqueous solution of glycogen in the presence of HPW and HSiW also yielded glucose. Thus, heteropoly acids are efficient, environmentally friendly and reusable catalysts for the conversion of glycogen to glucose.

A catalytic process for the selective conversion of carbohydrates to levulinic acid is developed. A synergy in the catalytic action is observed when a combination of ZnBr2 and HCl was used as the catalyst which is attributed to the in situ generation of HBr. Carbohydrates, namely, glucose, molasses and sucrose, were employed as feedstock for levulinic acid production. Microwave irradiation of glucose either in the presence of HCl alone or both HCl and ZnBr2 as catalysts yielded the formation of levulinic acid. But the conversion of glucose to levulinic acid was much faster (only 6 min) when both HCl and ZnBr2 were employed together. The effect of the reaction parameters like, the time of irradiation, % power, and amount of substrate and catalyst on the yield of levulinic acid were studied. The reaction products in each case were analysed using 1H and 13C NMR. The yield of levulinic acid was estimated using HPLC. The maximum yield of levulinic acid obtained from glucose was 53 wt%.

Ulva rigida, a common green seaweed, was used as a feedstock for the production of bioethanol in a simultaneous saccharification and fermentation (SSF) process carried out under sonication. Sonication provided a faster way for the simultaneous release of glucose from Ulva rigida and its conversion into bioethanol. Within 3 h, 196 ± 2.5 mg glucose per gram of dry weight of biomass and 333.3 ± 4.7 mg bioethanol per gram of glucose were produced in the SSF process under sonication. In addition to being fast, the process was devoid of any chemical pretreatment and involves only a single stage of sonication for the release of glucose from algae by the action of enzymes and also for the simultaneous fermentation of glucose to ethanol using Saccharomyces cerevisiae.

Macro algal seaweeds are a promising feedstock for biofuels production. Yet, their relatively low fermentable carbohydrate content and the inefficient methods used for their conversion hamper their utilization. The optimized production of Ulva rigida co-cultured with fed-fish in an offshore mariculture (fish cages) system is reported. Enhanced production of biomass with elevated content of desired carbohydrates is achieved. The farmed biomass was further converted to bioethanol by a one-step sonication assisted SSF process. An ethanol yield of 16 wt% (based on the dry weight of algae) is obtained.

Hydrolysis of biomass for the production of glucose was studied. Silicotungstic acid (HSiW) was deposited on graphene by an ultrasound-assisted procedure. The catalyst (HSiW/G) was characterized using a variety of physico-chemical methods. Homogeneous distribution of HSiW on the surface of graphene was demonstrated. The hydrolysis of glycogen was performed with a HSiW/G catalyst by hydrothermal treatment. The yield of glucose (66 wt%) obtained was about 8 times higher than that obtained with the same amount of bare HSiW. Stability of the HSiW/graphene even after 3 repeated uses was confirmed. The mechanism of the enhancement of catalytic activity was discussed in terms of a special interaction between the graphene support and HSiW and also the appearance of hydrophobic cavities on the surface of graphene. The formation of these cavities facilitates the anchoring of glycogen to the catalyst surface and promotes the attack of protons that leads to selective, rapid, and efficient hydrolysis.

Cellulose (Avicel®) is converted to potentially useful products (formic acid, ethylene glycol, and lactic acid). Isosaccharinic acid is identified as the reaction intermediate. Homogeneous aqueous dispersions of cellulose were obtained with the aid of sonication (1 h.). The degradation of the cellulose dispersion was carried out in an alkaline (NaOH) medium under microwave (domestic) irradiation conditions. With 1, 4 and 10 wt. % cellulose dispersions, conversion values of 44, 58 and 54 wt. %, respectively, were observed upon 5 min. of microwave irradiation. The reaction products in each case have been analyzed by 1 H and 13C NMR.

Bioethanol is a promising substitute for conventional fossil fuels. The focus of this work was to convert commercial cellulose (Avicel ® PH-101) to ethanol. In the first step, cellulose was selectively converted to glucose. Cellulose hydrolysis was carried out under microwave irradiation using hydrochloric acid as catalyst. Process parameters – acid concentration, irradiation time, and power consumption – were optimized. A yield of 0.67 g glucose/g cellulose was achieved under modest reaction conditions (2.38 M acid concentration, irradiation time – 7 min, 70% of power consumption). The glucose thus produced was then converted to ethanol by fermention with yeast ( Saccharomyces cerevisiae ). The speed, selective nature of the process and the attractive overall yield indicate that cellulose, a vast carbohydrate source, could indeed be a sustainable feedstock for bioethanol production.

Selective chemical reduction of carbon dioxide to formate anion under microwave irradiation is reported. No formaldehyde or methanol was generated as by products of the CO 2 reduction making the process highly selective. (NH 4 ) 2 CO 3 or dry ice was employed as CO 2 source. NaBH 4 is used as reducing agent. Aqueous solutions of (NH 4 ) 2 CO 3 or dry ice and NaBH 4 were subjected to microwave irradiation for a short duration of 5 min. The formation of formate is unequivocally established from the 1 H, 13 C and DEPT-135 NMR spectroscopic studies. FT-IR and UV–vis have been employed as auxiliary tools to observe the presence of formate ions. The obtained formate has the potential to be used as fuel in fuel cells or in turn can be converted to alkanes or can be used as a precursor for the production of hydrogen. Thus the current process is highly significant for the energy sector and to the chemical industry as well.

Nanospherical cellulose containers (SCC) (average size, ∼50 nm) are prepared by the sonochemical method. Organic and water-soluble materials are encapsulated within the SCC using only microcrystalline cellulose (MCC), an organic solvent, and water. Using silicotungstic acid (H4SiW12O40), the prepared SCCs can be catalytically converted (78 wt % conversion) to glucose (30 wt % glucose yield) by applying microwave irradiation for only 3 min. These results are attributed to the large increase of surface area of the cellulose sphere relative to MCC, and a better contact with the solid catalyst. Sealed in a vessel, SCCs were found stable for more than 6 months when stored at 4 °C or at room temperature. The encapsulation efficiency of the organic phase was measured and found to be approximately 90%. The creation of the sphere involves the degradation of the MCC to smaller fragments by high-intensity ultrasound irradiation, and the organization of these fragments in nanospheres involves the formation of bonds o...

Levulinic acid is a key platform chemical. Even gasoline range chemicals could be produced from levulinic acid making it a strategically significant compound. Producing levulinic acid from biomass is attractive from economic as well as environmental aspects. An acid catalyzed hydrothermal process for converting biomass to levulinic acid is reported. The effect of biomass type, acid (HCl) concentration, and reaction temperature of hydrothermal treatment on the conversion of biomass and yield of levulinic acid were studied. Widely available cellulosic biomass and agricultural wastes, namely, Cicer arietinum, cotton, Pinus radiata and sugarcane bagasse were successfully converted to levulinic acid. Although HPCL analysis could not be performed, qualitative and quantitative analysis of levulinic acid was conducted using 13C and 1H NMR spectroscopy. Under optimal reaction conditions (423 K, 1 M HCl, 2 h) the yields of levulinic acid obtained from Cicer arietinum, cotton, Pinus radiata and sugarcane bagasse were 32.6, 44.0, 19.0 and 36.5 wt%.

This report presents a method for producing large quantities of biodiesel from waste cooking oil (WCO). Preliminary studies on optimization of the WCO transesterification process in a continuous-flow microwave reactor are carried out using commercial SrO as a catalyst. The SrO catalyst can be separated and reused for five reaction cycles without loss in activity. Challenges like mass flow and pressure drop constraints need to be surmounted. SrO nanoparticles deposited on millimeter-sized (3–6 mm) silica beads (41 wt% SrO/SiO 2 ) are prepared and evaluated as a substitute for the SrO catalyst. A WCO conversion value to biodiesel as high as 99.2 wt% was achieved with the reactor packed with 15 g of 41 wt% SrO/SiO 2 catalyst in 8.2 min with 820 mL of feed. Excellent performance of the fixed-bed catalyst without loss in activity for a lifetime of 24.6 min converting a feed of 2.46 L to FAME was observed.

Currently, fermentation is the only available pathway for converting carbohydrates to ethanol and it is often time-consuming. The focus of the current research is to expedite ethanol production from carbohydrates using Saccharomyces cerevisiae. This study evaluated fermentation using a high-speed stirrer (ultraturrax) where glucose was the model carbohydrate. The reaction kinetics of fermentation was evaluated using 13C NMR spectroscopy. The effect of stirring speed on the kinetics of glucose fermentation was studied and two times enhancement in the rate of fermentation was observed using an ultraturrax (3.80 ± 0.40 × 10-5 s-1) compared to the incubation (1.90 ± 0.71 × 10-5 s-1) at 30°C. The acceleration of the fermentation was also observed using other carbohydrates such as sucrose and molasses. We report the effect of varying a few parameters such as: stirring speed, the effect of shelf-life of yeast, pH of the broth, and effect of activated carbon on the fermentation kinetics. The optimum pH range for the fermentation reaction was found to be 4-6.8. Yeast with a six-month shelf-life was found to slow down the fermentation reaction by 5.6 times relative to fresh yeast (up to one month). Our results indicate an efficient method for bioethanol production from carbohydrates.

Energy crisis and environmental deterioration are the twin problems facing the mankind. Alternate energy sources, especially, biofuels (biodiesel and bioethanol) produced from renewable sources like biomass would alleviate the problem to some extent. Fast and demand based production of biofuels is the need of the hour. Transesterification is the crucial chemical reaction for biodeisel production. Likewise, biomass pretreatment, hydrolysis of carbohydrates and fermentation of sugars are vital in bioethanol production. Interestingly, both the unconventional techniques, sonication and microwave irradiation were found to be extremely useful in accelerating the afore mentioned reactions holding a promise for making sustainable biorefinery possible. The present chapter fully covered the work on carrying out the biodiesel synthesis employing Sonochemistry , however, the use of MW radiation for the synthesis of biodiesel was limited to solid base catalysts. The second part of the chapter was devoted to the use of MW and sonochemistry for the synthesis of bioethanol.