Mass-Based Environmental Factor and Energy Assessment of Microwave-Assisted Synthesized Transition Metal Nanostructures

This paper describes mass-based energy phase-space projection of microwave-assisted synthesis of transition metals (zinc oxide, palladium, silver, platinum, and gold) nanostructures. The projection uses process energy budget (measured in kJ) on the horizontal axes and process density (measured in kJg−1) on the vertical axes. These two axes allow both mass usage efficiency (Environmental-Factor) and energy efficiency to be evaluated for a range of microwave applicator and metal synthesis. The metrics are allied to the: second, sixth and eleventh principle of the twelve principle of Green Chemistry. This analytical approach to microwave synthesis (widely considered as a useful Green Chemistry energy source) allows a quantified dynamic environmental quotient to be given to renewable plant-based biomass associated with the reduction of the metal precursors. Thus allowing a degree of quantification of claimed “eco-friendly” and “sustainable” synthesis with regard to waste production and energy usage.

Microwave-Assisted Au and Ag Nanoparticle Synthesis: An Energy Phase-Space Projection Analysis

Microwave-assisted synthesis of gold and silver nanoparticles, as a function of Green Chemistry, non Green Chemistry, and four applicator types are reported. The applicator types are Domestic microwave ovens, commercial temperature controlled microwave chemistry ovens (TCMC), digesters, and axial field helical antennae. For each of these microwave applicators the process energy budget where estimated (Watts multiplied by process time = kJ) and energy density (applied energy divided by suspension volume = kJ·ml-1) range between 180 ± 176.8 kJ, and 79.5 ± 79 kJ·ml-1, respectively. The axial field helical field an-tenna applicator is found to be the most energy efficient (0.253 kJ·m-1 per kJ, at 36 W). Followed by microwave ovens (4.47 ± 3.9 kJ·ml-1 per 76.83 ± 39 kJ), and TCMC ovens (2.86 ± 2.3 kJ·m-1 per 343 ± 321.5 kJ). The digester applicators have the least energy efficiency (36.2 ± 50.7 kJ·m-1 per 1010 ± 620 kJ). A comparison with reconstructed ‘non-thermal’ microwave oven inactivation microorganism experiments yields a power-law signature of n = 0.846 (R2 = 0.7923) four orders of magnitude. The paper provides a discussion on the Au and Ag nanoparticle chemistry and bio-chemistry synthesis aspects of the microwave applicator energy datasets and variation within each dataset. The visual and analytical approach within the energy phase-space projection enables a nanoparticle synthesis route to be systematically characterized, and where changes to the synthesis are to be mapped and compared directly with historical datasets. In order to help identify lower cost nanoparticle synthesis, in addition to potentially reduce synthesis energy to routes informed changes to potentially reduce synthesis energy budget, along with nanoparticle morphology and yield.

Green Chemistry Allometry Test of Microwave-Assisted Synthesis of Transition Metal Nanostructures

Microwave irradiation is considered an important approach to Green Chemistry, because of its ability to rapidly increase the internal temperature of polar-organic compounds that lead to synthesis times of minutes rather than hours when compared to conventional thermal heating. This works describes a dual allometry test for the discrimination between the solvents and reagents used in the microwave-assisted synthesis of transition metal (zinc oxide, palladium silver, platinum, and gold) nanostructures. The test is performed in log-log process energy phase-space projection, where the synthesis data (kJ against kJ·mol-1) has a power-law signature. The test is shown to discriminate between recommended Green Chemistry, problematic Green Chemistry, and Green Chemistry hazardous solvents. Typically, recommended Green chemistry exhibits a broad y-axes distribution within an upper exponent = 1 and lower exponent = 0.5. Problematic Green Chemistry exhibits a y-axes narrower distribution with an upper exponent = 0.94 and lower exponent = 0.64. Non-Green Chemistry hazardous data exhibits a further narrowing of the y-axes distribution within upper exponent = 0.87 and lower exponent = 0.66. In all three cases, the y-axes is aligned to original database power-law signature. It is also shown that in the x-axes direction (process energy budget) the grouped order of magnitude decreases from four orders for recommended Green Chemistry solvent and reagent data, through two orders for non-Green Chemistry hazardous material and down to one order for problematic Green Chemistry.

Microwave-Assisted Transition Metal Nanostructure Synthesis: Power-Law Signature Verification

A power-law (y = cxn) signature between process energy budget (kJ) and process energy density (kJ·ml-1) of microwave-assisted synthesis of silver and gold nanostructures has been recently described [Law and Denis. AJAC, 14(4), 149-174, (2023)]. This study explores this relation further for palladium, platinum, and zinc oxide nanostructures. Parametric cluster analysis and statistical analysis is used to test the power-law signature of over four orders of magnitude as a function of six microwave applicator-types metal precursor, non-Green Chemistry synthesis and claimed Green Chemistry. It is found that for the claimed Green Chemistry, process energy budget ranges from 0.291 to 900 kJ, with a residual error ranging between −33 to +25.9 kJ·ml-1. The non-Green Chemistry synthesis has a higher process energy budget range from 3.2 kJ to 3.3 MJ, with a residual error of −33.3 to +245.3 kJ·ml-1. It is also found that the energy profile over time produced by software controlled digestion applicators is poorly reported which leads to residual error problematic outliers that produce possible phase-transition in the power-law signature. The original Au and Ag database and new Pd, Pt and ZnO database (with and without problematic outliers) yield a global microwave-assisted synthesis power-law signature constants of c = 0.7172 ± 0.3214 kJ·ml-1 at x-axes = 0.001 kJ, and the exponent, n = 0.791 ± 0.055. The information in this study is aimed to understand variations in historical microwave-assisted synthesis processes, and develop new scale-out synthesis through process intensification.

Effect of Process Parameters of Microwave Assisted Extraction (MAE) on Polysaccharides Yield from Pumpkin

Process parameters of microwave assisted extraction （MAE） of the polysaccharides from pumpkin viz. extraction temperature, time and liquid-solid ratio were studied by using single factor and response surface methodology method. The results showed that the liquid-solid ratio was the most important factor in polysaccharides yield, followed the extraction temperature was the least important factor. The optimum microwave assisted extraction co by ndi extraction time, and tions for the highest polysaccharides yield from pumpkin （16.76%-4-0.38%） were obtained by using the response surface methodology with extraction time of 29 min, an extraction temperature of 79 ℃ and a liquid-solid ratio of 22 mL·g^-1. Validation experiment result well agreed with predicted value.

The influence of microwave irradiation on rocks for microwaveassisted underground excavation

Demand is growing for explosive-free rock breakage systems for civil and mining engineering, and space industry applications. This paper highlights the work being undertaken in the Geomechanics Laboratory of Mc Gill University to make a real application of microwave-assisted mechanical rock breakage to fullface tunneling machines and drilling. Comprehensive laboratory tests investigated the effect of microwave radiation on temperature profiles and strength reduction in hard rocks(norite, granite, and basalt)for a range of exposure times and microwave power levels. The heating rate on the surface of the rock specimens linearly decreased with distance between the sample and the microwave antenna, regardless of microwave power level and exposure time. Tensile and uniaxial compressive strengths were reduced with increasing exposure time and power level. Scanning electron micrographs(SEMs) highlighted fracture development in treated basalt. It was concluded that the microwave power level has a strong positive influence on the amount of heat damage induced to the rock surface. Numerical simulations of electric field intensity and wave propagation conducted with COMSOL Multiphysics~ software generated temperature profiles that were in close agreement with experimental results.

ITO nano-powders prepared by microwave-assisted co-precipitation in aqueous phase

By using microwave-assisted co-precipitation in aqueous phase, adding surface activation agent PEG-6000 into the mixture of InCl3 solution and SnCl4 solution, and dropping the ammonia solution with the density (volume ratio) of 1-0 to 1-4, ITO precursor was prepared at different reaction system temperatures of 35 ℃-85 ℃, then ITO nano-powder was obtained after it was calcinated at 800 ℃ for 1 h. The morphology of ITO nano-powder was characterized by SEM and its electrical conductivity was determined by conductivity meter. The effects of different temperatures and ammonia concentration in microwave-assisted reaction system on its morphology and electric conductivity were discussed. The experimental results indicate that with the dilution of the ammonia solution or the rise of reacting system temperature, the morphology of ITO particles is transformed from spherical to rod-like one with the decline of its electric conductivity. And the electric conductivity of ITO nano-powders with spherical morphology is higher than that of ITO nano-powders with rod-like morphology.

MICROWAVE-ASSISTED EXTRACTION OF GLYCYRRHIZIC ACID FROM LICORICE ROOT-EFFECT OF THE PROPERTY OF SOLUTION ON EXTRACTION OF GA

The property of extraction solution is an important factor influencing the extraction efficiency. In the present work, the effect of the property of solution on extraction of GA was studied, which including the concentration of ethanol, ammonia and cation (M+), pH of extraction solution, different kinds of organic solvent etc. The results show that 50%-60%(v/v) ethanol can reach high percentage extraction of GA. If 1% (v/v) ammonia solution was added into 60%(v/v) ethanol, the percentage extraction can be increased from 2.0% to 2.31%. Without ammonia, 50mmol/L [M+] (M+ = K+, NH4+) was added into 60%(v/v) ethanol, percentage extraction of GA can reach about 2.26%. If pH of solution (60% ethanol) was adjust to pH=4.0, it can reach high percentage extraction. If pH of solution (60% ethanol + 50mmol [M+], pH=6.1) was adjust tO PH=4.0, especially M+ is K+ or NH4+, it can reach almost same extraction efficiency as that of 1% ammonia solution + 60% ethanol, and the operation environment can be greatly improved.

Microwave Assisted Sintering and Photoluminescence Properties of BaaSi6OleNe：Eu^2＋ Green Phosphors

Eu^2＋-doped Ba3Si6012N2 green phosphors were prepared by microwave assisted sintering method at 1275℃ for 4 h, while the counterparts using conventional solid-state reaction method were synthesized at temperature higher than 1300℃ and for to 10 h. Microwave assisted sintering could reduce the activation energy and enhance the diffu- sion rate, thus greatly improved the sintering. Moreover, the influence of Si3N4 content on phase formation, morphol- ogy, absorption, and quantum efficiency, and photoluminescence properties of phosphors were studied. As a result, the Ba3Si6OI2N2：Eu^2＋ samples sintered by microwave assisted sintering method have a higher phase purity and photo- luminescence intensity under ultraviolet excitation as compared with samples sintered in the conventional tube furnace The proposed method is a potential preparation method for the oxynitride phosphors with strong photoluminescence and high phase purity.

Microwave-Assisted Alkaline Pretreatment and Microwave Assisted Enzymatic Saccharification of Oil Palm Empty Fruit Bunch Fiber for Enhanced Fermentable Sugar Yield

Lignocellulosic materials are promising alternative feedstocks for bioethanol production. However, the recalcitrant nature of lignocellulosic biomass necessitates an efficient pretreatment pretreatment step to improve the yield of fermentable sugars and maximizing the enzymatic hydrolysis efficiency. Microwave pretreatment may be a good alternative as it can reduce the pretreatment time and improve the enzymatic activity during hydrolysis. The overall goal of this paper is to expand the current state of knowledge on microwave-based pretreatment of lignocellulosic biomass and microwave assisted enzymatic reaction or Microwave Irradiation-Enzyme Coupling Catalysis (MIECC). In the present study, a comparison of microwave assisted alkali pretreatment was tried using Oil Palm empty fruit bunch. The microwave assisted alkali pretreatment of EFB using NaOH, significantly improved the enzymatic saccharification of EFB by removing more lignin and hemicellulose and increasing its accessibility to hydrolytic enzymes. The results showed that the optimum pretreatment condition was 3% (w/v) NaOH at 180 W for 12 minutes with the optimum component loss of lignin and holocellulose of about 74% and 24.5% respectively. The subsequent enzymatic saccharification of EFB pretreated by microwave assisted NaOH (3% w/v);resulted in 411 mg of reducing sugar per gram EFB at cellulose enzyme dosage of 20 FPU. The overall enhancement by the microwave treatment during the microwave assisted alkali pretreatment and microwave assisted enzymatic hydrolysis was 5.8 fold. The present study has highlighted the importance of well controlled microwave assisted enzymatic reaction to enhance the overall reaction rate of the process.

Low temperature microwave-assisted vs conventional pyrolysis of various biomass feedstocks

A comparison between conventional pyrolysis and a novel developed low-temperature microwave-assisted pyrolysis methodology has been performed for the valorisation of a range of biomass feedstocks including waste residues. Microwave pyrolysis was found to efficiently deliver comparable evolution of bio-gases in the system as compared with conventional pyrolysis at significantly reduced temperatures （120-180 ℃vs 250-400 ℃）. The gas obtained from microwave-assisted pyrolysis was found to contain CO2, CH4 and CO as major components as well

Microwave-assisted Extraction of Rutin and Quercetin from Flos Sophorae

Three microwave-assisted extraction(MAE) procedures were studied. The first procedure was household microwave oven dynamic extraction(HMODE). The second procedure was special microwave oven bath extraction(SMOBE). The third procedure was microwave resonant cavity dynamic extraction(MRCDE). The results obtained by the three microwave-assisted extraction procedures were compared with those obtained by using traditional Soxhlet extraction. The results indicate that the MAE not only took a shorter time, but also simplified the procedure, and made the extraction a higher yield. At the same time the results obtained by the three MAE procedures were also compared with each other.

Microwave-assisted synthesis and characterization of ZnO-nanorod arrays

High density ZnO-nanorod arrays(rod length 1.59μm)were successfully synthesized via a microwave-assisted solution-phase method using zinc chloride and ammonia solution as reactants.The influence of concentration of ammonia solution, work power,and microwave irradiation time on the morphology and size of final products was carefully investigated.The crystal structure,chemical composition and morphologies of final products were characterized using X-ray powder diffraction(XRD), scanning electron microscopy(SEM)and photoluminescence(PL).The as-synthesized ZnO is composed of single crystalline and possesses three photoluminescence emissions centered at 400,469 and 534.5 nm,respectively.

Optimization of microwave-assisted extraction of bioactive alkaloids from lotus plumule using response surface methodology

In this work,a fast and efficient microwave-assisted extraction(MAE) method was developed to extract main bioactive alkaloids from lotus plumue.To optimize MAE conditions,three main factors were selected using univariate approach experiments,and then central composite design(CCD).The optimal extraction conditions were as follows:methanol concentration of 65%,microwave power of 200 W,and extraction time of 260 s.A high performance liquid chromatography–diode array detector(HPLC–DAD) method was established to quantitatively analyze these phytochemicals in different lotus plumule samples and in different part of lotus.Chromatographic separation was carried out on an Agilent Zorbax Extend-C_(18) column(4.6 mm×150 mm,3.5 μm).Gradient elution was applied with the mobile phase constituted with 0.1% triethylamine in water(A)and acetonitrile(B):40%-70% B at 0-8 min,70%-100% B at 8–9 min,100% B for 2 min,and then equilibrated with 40% B for 2 min.

Catalytic performance and synthesis of a Pt/graphene-TiO_2 catalyst using an environmentally friendly microwave-assisted solvothermal method

A Pt/graphene‐TiO2catalyst was prepared by a microwave‐assisted solvothermal method and was characterized by X‐ray diffraction,scanning electron microscopy,transmission electron microscopy,cyclic voltammetry,and linear sweep voltammetry.The cubic TiO2particles were approximately60nm in size and were distributed on the graphene sheets.The Pt nanoparticles were uniformly distributed between the TiO2particles and the graphene sheet.The catalyst exhibited a significant improvement in activity and stability towards the oxygen reduction reaction compared with Pt/C,which resulted from the high electronic conductivity of graphene and strong metal‐support interactions.

Microwave-assisted solvent extraction of castor oil from castor seeds

This study was aimed at evaluating the physicochemical properties and oxidation stability of castor oil using microwave-assisted solvent extraction(MAE). MAE was performed using 5% ethanol in hexane as solvent at different extraction times, power intensities and solvent-to-feed(S/F, ml of solvent to gram of feed) ratios.The process parameters were optimized by statistical approach using historical data design of response surface method(RSM). The oils were characterized for yield, physicochemical properties, dielectric properties and oxidation stability, and comparison was also made with oil extracted using Soxhlet method. Results show that the maximum oil yield of 37% was obtained at 20 min with microwave power intensity of 330 W and S/F ratio of 20. The main fatty acid composition of castor oil is ricinoleic acid. The density, refractive index, dielectric properties and oxidation stability of oils are not affected by the extraction methods and extraction parameters of MAE. However, the MAE-extracted oil is more viscous compared to that by Soxhlet method. With extra caution on oil oxidation, MAE could be a promising solvent extraction method with an 86% less in processing time and a higher yield.

Microwave-assisted Polymerization of D,L-Lactide with Stannous Octanoate as Catalyst

Poly (lactic acid) (PLA) was synthesized by microwave-assisted ring-opening polymerization of D, L-lactide with stannous octanoate (SnOct(2)) as catalyst. Its weight-average molar mass (M-w) ranged from 39000 to 67000 and the polydispersity index from 1.3 to 1.7. The polymerization rate was much faster than that of the conventional thermal polymerization. A degradation of newly formed PLA in reaction mixture by microwave irradiation was observed.

Green evaluation of microwave-assisted leaching process of high titanium slag on life cycle assessment

A greenness evaluation index and system of microwave-assisted leaching method were established.The effects of the life cycle assessment variables,such as the resource consumption,environment impact,cost,time and quality,were investigated,and the concept of green degree was applied in the production of synthetic rutile.An analytic hierarchy process was utilized to assess matrix of greenness evaluation.The Gauss-Seidel iterative matrix method was employed to solve the assessment matrix and obtain the weights and membership functions of all evaluation indexes.A fuzzy decision-making method was applied to build the greenness evaluation model,and then the scores of green degree in microwave-assisted leaching process was obtained.The greenness evaluation model was applied to the life cycle assessment of the microwave-assisted leaching process.The results show that the microwave-assisted leaching process has advantages over the conventional ones,with respect to energy-consumption,processing time and environmental protection.

Response surface optimization of microwave-assisted extraction for HPLC-fluorescence determination of puerarin and daidzein in Radix Puerariae thomsonii

Microwave-assisted extraction was optimized with response surface methodology for HPLC-fluorescence determination of puerarin and daidzein in Radix Puerariae thomsonii.The optimized extraction procedure was achieved by soaking the sample with 70% methanol（1∶15,v/v）for 30 min,and then microwave irradiation for 11 min at a power of 600 W.Coupling the extraction process with HPLC-fluorescence presented good recovery,satisfactory precision,and good linear relation.Compared with a method from the Chinese Pharmacopoeia,the proposed method enables higher extraction efficiency and more accurate analytical results.It can be of potential value in quality assessment of Radix Puerariae thomsonii medicinal materials.

Microwave-assisted Kornblum oxidation of organic halides

Microwave-assisted Kornblum oxidation is proved to be an effective way to obtain aldehyde and ketones from their corresponding chlorides. Under microwave irradiation, not only the reaction time was greatly decreased, due to avoiding the by-product, the yield was increased. It is noteworthy that the scope of the method was broadly expanded.