Microwave Assistance Research Articles

NaOH-Promoted Reduction of Carbonyl Compounds Assisted by Microwave

The reduction of aldehydes and ketones based on MPV chemistry is one of the vital transformations in organic chemistry. In this study, MPV chemistry was developed in heating assistance of Microwave to synthesize a broad range of alcohol with yields up to 96 % by a simple, cheap, and safe synthetic protocol. Sodium hydroxide (NaOH) is an excellent promoter for the reduction. The method is quite cheap and straightforward while it utilized easy-to-handle chemicals and did not require strictly anhydrous reagents, transition metals, or any additional ligands. This potential method encourages a scale-up upgrading of Microwave use for alcohol production.

Synthesis and spectroscopic characterization of CsPbBr3/Cs4PbBr6 perovskites synthesized via the microwave-assisted heating process for backlight display devices

Abstract In this study, CsPbBr3/Cs4PbBr6 composites were prepared via microwave-assisted (MA) and conventional heating (CH) routes. X-ray diffraction and high-resolution transmission electron microscopy confirmed the coexistence of CsPbBr3 and Cs4PbBr6 phases in the prepared samples. The steady-state absorption spectra of the synthesized perovskites exhibited excitonic peaks at 310 and 525 nm because of the absorption of Cs4PbBr6 and CsPbBr3, respectively. The prepared samples exhibited characteristic emission peaks at approximately 523 nm. The MA-derived sample exhibited high color purity (94%), high quantum yield (89%), and good thermal stability (>98% after 100 h of treatment). By contrast, the CH-derived sample exhibited low color purity (91%) and quantum yield (70%). Furthermore, microwave irradiation with polar molecules in MA heating resulted in the rapid generation of homogeneous heat within the heated materials, which induced the substantial nucleation and growth of CsPbBr3. This phenomenon enhanced intensity of photoluminescence emission. The MA-derived sample exhibited a shorter excitonic lifetime (20 ns) than the CH-derived sample did (32 ns) because the MA-derived sample had less nonradiative trap sites. The color gamut of the as-prepared light-emitting devices fabricated with the MA-derived sample was 125% of the NTSC. This study indicated that the incorporation of microwave heating in the synthesis process is an effective approach for preparing CsPbBr3/Cs4PbBr6 composites with a wide color gamut, good thermal stability, and a PLQY.

Effect of N,N′-dimethylformamide solvent on structure and thermal properties of lanthanide(III) complexes with flexible biphenyl-4,4′-dioxydiacetic acid

The N,N′-dimethylformamide (DMF) was used in the microwave-assisted (MW) solvothermal method for the preparation of lanthanide(III) complexes with biphenyl-4,4′-dioxydiacetic acid (H2L) of the formula Ln2L3·xDMF⋅yH2O where Ln = lanthanide(III) ions from La(III) to Lu(III) with the Pm(III) exception x = 1.5–3; y = 2 for Yb and Lu or 0 for the remaining complexes and L = C14H12O2(COO) 2 2− . The obtained complexes were characterized by the elemental analysis, infrared spectroscopy (ATR-FTIR), X-ray diffraction patterns and different methods (TG-DSC and TG-FTIR) of thermal analysis. Crystalline complexes contain N,N′-dimethylformamide molecules in their structures. Additionally, water molecules are present in the structures of Yb(III) and Lu(III) complexes. Coordination of lanthanide ions occurs through carboxylate oxygen atoms from the biphenyl-4,4′-dioxydiacetate ligand and most probably carbonyl oxygen atom from N,N′-dimethylformamide. The investigated compounds exhibit different thermal stability, and removal of solvent molecules takes place in a more complex way in the group of heavy lanthanide complexes. Their desolvated forms are an unstable [except Yb(Lu)2L3 compounds], and their further heating leads to the formation of suitable lanthanide oxides (air atmosphere). Thermal stability of the investigated compounds is higher in nitrogen atmosphere. The TG-FTIR methods allowed to propose way of thermal decomposition of investigated compounds through identification of volatile products such as: DMF, H2O, CO2, CO and CH4 evolved during heating of complexes. The luminescent properties of terbium(III) and europium(III) complexes were also investigated.

Investigation on the use of deep eutectic solvent with microwave assistance for the extraction of ferulic acid from palm pressed fibre

Ferulic acid is a highly sought-after compound as functional food and nutraceuticals due to its antioxidative, anti-microbial and anti-inflammatory properties. Extraction of ferulic acid from oil palm pressed fibre by using microwave assisted deep eutectic solvent (DES) extraction was studied and reported. The influence of water content in the DES, microwave irradiation temperature and duration on the extraction efficiency were investigated. The viscosity of the DES of ChCl-AA, reduced from 9.678 ​mm2/s to 5.7356 ​mm2/s as the water content in the DES increased from 0% to 10% (v/v). DES with 30% (v/v) water (viscosity 2.547 ​mm2/s) was found to be optimal for ferulic acid extraction. The amount of ferulic acid extracted under microwave heating at 60 ​°C for 9 ​min were 0.609 ​mg/g – 0.617 ​mg/g and up to 1.123 ​mg/g when heated for 15 ​min. Response surface method showed that the microwave assisted DES extraction of ferulic acid from palm pressed fibre depended on the microwave temperature, heating duration and the interaction between the heating temperature and duration.

Comparison of various synthesis methods and synthesis parameters of pyrazoline derivates.

Pyrazoline plays an important role in the development of heterocyclic chemistry theory and is widely used as a synthesis useful in organic synthesis. The structure of the pyrazoline derivative compound contains a 5-membered heterocyclic framework with two nitrogen atoms and one endocyclic double bond. The function of pyrazoline as a fragment was stable enough in the bioactive group to synthesize new compounds with various biological activities. Various methods that could be used for the synthesis of pyrazole derivatives were ultrasonic irradiation, microwave assistance, ionic liquids, grinding techniques, and conventional methods. However, the synthesis of pyrazoline derivatives using conventional methods had many problems, one of which is the product yield, which was <70%. Therefore, this article will discuss the importance of optimizing the synthesis reaction conditions by taking into account several synthesis parameters to get the best organic product results based on conventional methods. A literature search was conducted by employing PubChem, Chemspider Google Scholar, Research Gate, Science Direct, and Elsevier by selecting pyrazoline synthesis based on physicochemical profile, reaction mechanism, and synthesis method.

Direct oxidation of N-ynylsulfonamides into N-sulfonyloxoacetamides with DMSO as a nucleophilic oxidant.

N-Arylethynylsulfonamides are oxidized into N-sulfonyl-2-aryloxoacetamides directly and efficiently with dimethyl sulfoxide (DMSO) as both an oxidant and solvent with microwave assistance. DFT calculations indicate that DMSO nucleophilically attacks the ethylic triple bond and transfers its oxygen atom to the triple bond to form zwitterionic anionic N-sulfonyliminiums to trigger the reaction. Then it nucleophilically attacks the generated iminium intermediates to accomplish the oxidation via the second oxygen atom transfer. The current method provides a straightforward and efficient strategy to transform various N-arylethynylsulfonamides into N-sulfonyl-2-aryloxoacetamides, sulfonyl oxoacetimides, without any other electrophilic activators or oxidants.

The Friedel-Crafts sulfonylation catalyzed by chloroaluminate ionic liquids

Friedel-Crafts sulfonylation is one of the most common methods to prepare sulfone. With the development of Green Chemistry, chemical processes have been improved towards being environmentally friendly by using of organic solvents in the limit, using recoverable catalysts, reducing energy ... are getting more attention. Therefore, in this study, several types of ionic liquids such as [Bmim]BF4, [Bmim]PF6, [Bpy]Cl2AlCl3, [Pyrro]I2AlCl3, [Mth]I2AlCl3, [Bmim]Cl2AlCl3 which catalysed for the Friedel-Crafts sulfonylation of toluene and benzenesulfonyl chloride have been investigated. Besides, most factors which have influenced on the reaction yield such as the temperature, the reaction time, the amount of catalyst have been studied. The reaction was carried out under solvent-free and mild conditions; moreover, the catalyst was able to be recovered and reused without significant loss of its activity. The main product phenyl p-tolyl sulfone was easily isolated after the reaction and obtained in high yield 97% after four-hour heating at 100 oC by using Nbutylpyridinium chloroaluminate, [Bpy]Cl.2AlCl3, as catalyst. Microwave irradiation has been used to improve many organic syntheses as a green and efficient activation method in order to reduce reaction times and save energy. Compared to the conventional heating, phenyl p-tolyl sulfone was synthesized with the excellent yield in the short reaction time under the microwave assistance.

A SnO2 shell for high environmental stability of Ag nanowires applied for thermal management.

Since silver nanowires (AgNWs) show high infrared reflectance many studies present their applicability as thermal management products for various wearable textiles. However, their use for practical purposes is only partially evaluated, without focusing on improving their low atmospheric and liquid stability. This report describes a new approach for the topic and proposes a facile method of Ag nanowire passivation with a SnO2 layer for high environmental stability and retention of high infrared reflectance. The one-step passivation process of AgNWs was carried out in the presence of sodium stannate in an aqueous solution at 100 °C, and resulted in the formation of core/shell Ag/SnO2 nanowires. This study presents the morphological, chemical, and structural properties of Ag/SnO2NWs formed with a 14 nm thick SnO2 shell, consisting of 7 nm rutile-type crystals, covering the silver metallic core. The optical properties of the AgNWs changed significantly after shell formation, and the longitudinal and transverse modes in the surface plasmon resonance spectrum were red shifted as a result of the surrounding media dielectric constant changes. The passivation process protected the AgNWs from decomposition in air for over 4 months, and from dissolution in a KCN solution at concentrations up to 0.1 wt%. Moreover, the report shows the microwave irradiation effect on the shell synthesis and previously synthesised Ag/SnO2NWs. The post-synthesis irradiation, as well as the SnO2 shell obtained by microwave assistance, did not allow long-term stability to be achieved. The microwave-assisted synthesis process was also not fast enough to inhibit the formation of prismatic silver structures from the nanowires. The Ag/SnO2NWs with a shell obtained by a simple hydrolysis process, apart from showing high infra-red reflectance on the para-aramid fabric, are highly environmentally stable. The presented SnO2 shell preparation method can protect the AgNW's surface from dissolution or decomposition and facilitate the designing of durable smart wearable thermal materials for various conditions.

Augmented Reality and the Novel Use of Indocyanine Green as a Navigational Adjunct for Laparoscopic Ablation of Liver Tumors

Introduction: Laparoscopy can be used as an adjunct to successfully treat hepatocellular carcinoma nodules, as the surgeon manipulates the liver under direct visualization. To successfully perform laparoscopic assisted thermal ablation the surgeon must be skilled at ultrasound to identify the tumor nodule(s). In this study we introduce a novel adjunct to laparoscopic assisted microwave ablation via IV infusion of indocyanine green (ICG) dye.

Regimes of hydrochar yield from hydrothermal degradation of various lignocellulosic biomass: A review

Hydrothermal carbonization (HTC) technique is used to convert lignocellulosic biomass into carbon-rich solid fuel. The product, hydrochar, finds a multitude of applications as a fuel, catalyst, adsorbent, etc. This paper reviews the different feedstock suitable for HTC that are experimentally investigated and classifies them into five categories like woody biomass, plant biomass, agricultural biomass, algae, and municipal solid waste (MSW). The operating regimes and hydrochar yields for each category are systematically reviewed and presented. With 75% hydrochar yield and high calorific value, the food waste of MSW makes an excellent candidate for HTC feedstock. The conversion mechanisms of each constituent of biomass are also discussed. Different parameters that significantly affect the process yield are temperature, residence time, pH, and, water to biomass ratio. Improvement in the quality of hydrochar can be attained by using the assistance of microwaves. Different characterization techniques are discussed briefly and energy content obtained in each type of feedstock is comprehensively presented. The best operating regime for the process having a temperature range of 180–240 °C with a slightly acidic pH in feed condition. Further rigorous and extensive research on surface characteristics and deactivation mechanism for catalyst/adsorbent applications is required to appropriately identify the suitable feedstock. Further research is also required to ascertain the behavior of other organic compounds, their degradation mechanism in biomass, and analyze the liquid and gaseous by-products obtained. • Biomass feedstock for HTC is categorized and the operating regimes are reviewed. • Feedstock and temperature considerably affects hydrochar yield and quality. • High hydrochar yields for any feedstock can be obtained between 180 and 220 °C. • Among all feedstock, food waste produces the highest yield with HHV of 30–33 MJ/kg. • Intermediate and by-products of HTC process needs further investigation.

Stable Isotope Dilution Analysis of the Major Prenylated Flavonoids Found in Beer, Hop Tea, and Hops.

Prenylated flavonoids from hops (Humulus lupulus) have become of interest in recent years due to a range of bioactivities. The potential health benefits of prenylated flavonoids include anti-cancerous activities and treatment of the metabolic syndrome among others. Since prenylated flavonoids from hops have shown pharmaceutical potential in clinical trials, robust analytical methods to determine their concentrations in food, supplements, and beverages are required. One such, the gold standard of analytical methods, is stable isotope dilution analysis due to its ability to compensate matrix effects and losses during sample work-up. As no commercial standards were available, the synthesis of seven different prenylated flavonoid isotopes utilizing various strategies (microwave assistance, acid base catalyst in the presence of deuterated substance and lastly, the use of Strykers catalyst) is described. The produced prenylated flavonoid isotopes were then applied in the first stable isotope dilution analysis method that quantified six natural prenylated flavonoids (Isoxanthohumol, Isoxanthohumol-C, 8-Prenylnaringenin, 6- Prenylnaringenin, Xanthohumol, and Xanthohumol-C) in beer, hop tea and hops to prove its applicability. The SIDA-LC-MS/MS method was validated resulting in LODs and LOQs for all analytes between 0.04 and 3.2 μg/L. Moreover, due to the simple clean-up the developed method allows the prospect for measuring clinical samples in the future.

P‐doped Carbon as the Efficient Support of Nickel Catalysts for Hydrodechlorination of Chlorodifluoromethane

AbstractP‐doped carbon material (P−C) is successfully fabricated through directly combust phytic acid via microwave assistant. Then the as‐made P−C is selected as the support to load various amount of Ni. As the evaluated results show that 5 %Ni/P−C exhibits better catalytic performance than 5 %Ni/C for chlorodifluoromethane hydrodechlorination (HDC) reaction. It is because that the doped‐P is feasible to promote the dispersion of Ni species on the surface of P−C through the strong interaction between Ni and the P−C support. Therefore, combining the synergetic effect between Ni and heteroatom‐doped carbon could provide a promising way to improve the activity of HDC reaction.

Microwave-aided synthesis of BiOI/g-C3N4 composites and their enhanced catalytic activities for Cr(VI) removal

Few-layer g-C3N4 nanosheets (CN-E) were synthesized by flash freezing the bulk g-C3N4 together with thermo-exfoliation with different time (2–20 min) by microwave assistant, to reduce the thickness of g-C3N4. Then, BiOI nanoflowers were grown in situ on CN-E by microwave-aided synthesis, forming BiOI/CN-E nanocomposites. The BiOI/CN-E showed a best activity of 27% improved Cr(VI) removal efficiency compared with the un-exfoliated BiOI/g-C3N4. The exfoliating CN-E coated on BiOI formed a heterojunction more efficiency than the two overlaid structure of g-C3N4 and BiOI, thus further improved the specific surface area and the catalytic performance during the treatment for pollutant Cr(VI).

Microwave-assisted alkali hydrolysis for cellulose isolation from wheat straw: Influence of reaction conditions and non-thermal effects of microwave

Microwave-assisted hydrolysis has been widely studied for cellulose fiber isolation, but the influence of reaction conditions and the microwave non-thermal effect are not well clarified. In this study, a series of well-designed experiments were carried out to measure the effects of reaction conditions including temperature, duration and alkali concentration. Compared to the other parameters, temperature was more relevant to the cellulose content in fiber. It could reach the maximum purity of 90.66 % when the temperature was up to 140 °C. Moreover, the existence of non-thermal effect of microwave has been confirmed through extensive determination and characterization of the fibers obtained from parallel controlled experiments conducted with or without microwave assistance. Approximately 50 %–75 % reduction in reaction time or 67 % of that in chemical costs would be realized under microwave with respect to traditional heating hydrolysis. Therefore, this work provides both deep insight and efficiency strategy into the microwave-assisted cellulose isolation.

A Comparative Study on the Thermoelectric Properties of Bismuth Chalcogenide Alloys Synthesized through Mechanochemical Alloying and Microwave-Assisted Solution Synthesis Routes

The way a material is synthesized and processed has an immense effect on its microstructure, which in turn has a big impact on its transport properties. Here we compare the thermoelectric (TE) properties of n- and p-type Bi2-xSbxTe3 (x: 0 and 1.5) materials synthesized through two different routes, specifically mechanochemical alloying (MA) -as a solid-state synthesis route, and microwave-assisted (MW) polyol synthesis -as a solution synthesis route. Reaction time is significantly reduced in the MW synthesis, leading to a significantly lower energy consumption (i.e. higher energy efficiency) per batch as compared to the MA route. The resultant materials are compared for their crystallinity, phase purity, morphology, and microstructure. Spark plasma sintering was used to prepare pellets and the resultant consolidates were evaluated for their transport properties. TE properties and microstructure of the specimens were investigated in relation to processing conditions and composition. MA samples formed fused structures (from 200 nm to several micrometers in size) composed of smaller particles. MW synthesized materials exhibit hexagonal platelet morphology, high crystallinity and phase purity. They also show lower thermal conductivity, leading to a higher resultant TE figure-of-merit -ZT. TE properties of Bi2-xSbxTe3 samples were studied on sintered cylindrical pellet samples, where the highest ZT values achieved were 1.04 (@ 440 K) for MW-Bi2Te3 and 0.76 (@ 523 K) for MW-Bi0.5Sb1.5Te3 samples, while MA-Bi2Te3 and MA-Bi0.5Sb1.5Te3 samples showed maximum ZT values of 0.74 (@ 460 K) and 0.27 (@ 300 K), respectively as n- and p-type TE materials. The observed trend is much higher ZT values for MW samples, ascribed to their higher degree of texturing and nanostructured grains reducing the thermal conductivity, thus achieving a better overall performance, verifying the prospect to enhance ZT using MW-assisted solution synthesis approach.

Microwave‐assisted deep eutectic solvent extraction of phenolic compounds from brewer's spent grain

AbstractBACKGROUNDDeep eutectic solvents (DESs) have been tested as promising green solvents for the microwave‐assisted extraction of phenolic compounds from brewer's spent grain (BSG). Firstly, a preliminary screening with four different DESs was carried out in order to determine the most effective DES for recovering phenolic compounds (measured as total phenols) from BSG. Later, an experimental design using the DES found to be most effective in the preliminary screening was applied to optimize microwave‐assisted choline chloride (ChCl):glycerol extraction.RESULTSChCl:glycerol was the most effective DES tested in the preliminary screening to recover phenolic compounds (2.3 mg GA g−1 BSG), even more than methanol (80% v/v) as conventional solvent (1.2 mg GA g−1 BSG). On the other hand, using ChCl:glycerol as DES, a total phenols content of 2.89 mg GA g−1 BSG was obtained operating at 100 °C for 13.30 min and 37.46% (v/v) water in the DES, ferulic and coumaric acids being the most abundant. Moreover, a residual extracted solid with non‐disturbed structural carbohydrates was achieved, which could be successfully used in a biorefinery to obtain other products, such as biofuels or chemicals.CONCLUSIONSThe suitability of a novel and green extraction process based on DESs combined with microwave assistance for the recovery of phenolic compounds from BSG was demonstrated. © 2020 Society of Chemical Industry (SCI)

Comparative study of Co3O4-ZSM-5 catalysts synthesized by different hydrothermal methods for the catalytic oxidation of dichloromethane

In this work, various Co3O4-ZSM-5 catalysts were prepared by the microwave hydrothermal method (MH-Co3O4@ZSM-5), dynamic hydrothermal method (DH-Co3O4@ZSM-5), and conventional hydrothermal method (CH-Co3O4/ZSM-5). Their catalytic oxidation of dichloromethane (DCM) was analyzed. Detailed characterizations such as X-ray diffractometer (XRD), scanning microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), H2 temperature-programmed reduction (H2-TPR), temperature-programmed desorption of O2 (O2-TPD), temperature-programmed desorption of NH3 (NH3-TPD), diffuse reflectance infrared Fourier-transform spectra with NH3 molecules (NH3-DRIFT), and temperature-programmed surface reaction (TPSR) were performed. Results showed that with the assistance of microwave, MH-Co3O4@ZSM-5 formed a uniform core-shell structure, while the other two samples did not. MH-Co3O4@ZSM-5 possessed rich surface adsorbed oxygen species, higher ratio of Co3+/Co2+, strong acidity, high reducibility, and oxygen mobility among the three Co3O4-ZSM-5 catalysts, which was beneficial for the improvement of DCM oxidation. In the oxidation of dichloromethane, MH-Co3O4@ZSM-5 presented the best activity and mineralization, which was consistent with the characterizations results. Meanwhile, according to the TPSR test, HCl or Cl2 removal from the catalyst surface was also promoted in MH-Co3O4@ZSM-5 by their abundant Brønsted acid sites and the promotion of Deacon reaction by Co3O4 or the synergistic effect of Co3O4 and ZSM-5. According to the results of in situ DRIFT studies, a possible reaction pathway of DCM oxidation was proposed over the MH-Co3O4@ZSM-5 catalysts.

Development and application of green and sustainable analytical methods for flavonoid extraction from Passiflora waste

Brazilian biodiversity and favourable environmental conditions open up possibilities not yet explored, showing potential to shift the country’s monochromatic economy into an emancipated, diversified and sustainable economic environment. This can be made possible through the integral use of its resources, exploring every functional fraction to create novel solutions to modern problems. Biorefineries present an interesting strategy to fully use the potential of agricultural feedstocks and together with green separation methods can contribute to the generation of sustainable processes and products. Passion Fruit (Passiflora edulis Sims f. flavicarpa Deg species) is produced on a large scale in Brazil and in other tropical countries, and its processing plants generate tons of residues that basically consist of peel, seeds and bagasse, which account for around 75% of its mass. These fractions of P. edulis can contain significant amounts of flavonoids, secondary metabolites that are the main compounds responsible for the fruit’s bioactivity (antioxidant, anti-inflammatory, pesticide and biocide, in general). Therefore, this work aims to develop, apply and compare the best conditions for the extraction of isoorientin, orientin and isovitexin from passion fruit applying solid–liquid methodologies, followed by analyte quantification using UHPLC-PDA. Homogenizer-assisted (HAE), ultrasound-assisted (UAE) and microwave-assisted (MAE) extraction techniques were used, as well as a full factorial design to reach optimal parameters concerning the extraction yield and energy and solvent efficiencies. According to the results, the procedure based on HAE presented the best conditions for the extraction of selected flavonoids (1.07, 0.90 and 0.33 mg g−1 of isoorientin, orientin and isovitexin, respectively) and was considered the best method according to the green and sustainable described factors.

Microwave-Assisted Hydrolysis of Cellulose in Towel and Wheat Straw Using Freeze-Thawing with NaOH

The aim of this study was to produce a high yield of direct hydrolysis of glucose from a cotton towel and wheat straw by microwave-assisted (MW) treatment. To this effect, a freeze-thawing with 3% NaOH was added before MW treatment. Multiple MW parameters were tested. For the towel, the highest glucose yield of 42.4% based on freeze-thawing with 3% NaOH-treated sample was observed after MW treatment at 200 °C for 30 s with 2% sulfuric acid as a catalyst. This corresponded to a 44.4% yield based on the cellulose content of treated samples, which was 1.3-fold higher than that of samples treated only by MW at 200 °C for 7 min with 1% sulfuric acid as a catalyst (maximum glucose yield in our previous report). For wheat straw, the highest glucose yield of 27.0% based on freeze-thawing with 3% NaOH-treated sample, and 41.9% based on the treated sample cellulose content were observed after MW treatment at 200 °C for 3 min with 0.5% sulfuric acid as a catalyst. Under the optimum conditions, the glucose yield was 40.5% from raw towel and 14.7% from wheat straw. Combined severity parameter analysis revealed that the addition of freeze-thawing with NaOH before the MW treatment increased the glucose yield and reduced the severity of the treatment conditions. In conclusion, freeze-thawing using 3% NaOH before MW treatment is effective for the direct hydrolysis of glucose from towels and wheat straw.

Microwave-assisted hydrothermal synthesis of copper oxide-based gas-sensitive nanostructures

Hydrothermal methods are widely used in chemical synthesis of target products with specific morphology and nanostructure. Those methods are very efficient for the preparation of well-controlled structures but the reaction time is usually long. The assistance of microwave makes the reaction system heat up faster, more uniformly and reactions are accelerated, it also can be utilized to change the morphology or structure of materials, which improves the physic-chemical properties of synthesized products and influences its gas-sensing performance. Copper oxide (CuO) is widely applied in semiconductor gas sensors because of its good reactivity and stability. This review article briefly introduces the principle, mechanism and recent development of CuO nanostructures obtained by microwave-assisted hydrothermal synthesis (MWHS) process. It also discussed the relation between endopathic factors of material and its gas-sensitive performance. The technical challenges and prospective solutions for high-performance CuO-based gas-sensitive materials with unique nanostructure are proposed. It is pointed out that the hierarchical CuO-based nanostructures and their composite materials prepared by MWHS process are efficacious methods to improve the gas-sensitive performance of the materials. On the basis of the morphology, the materials are divided into nanorods, nanoflowers, nanosheets, nanospheres and other nanostructures. The influence of microwave parameters on the properties of synthetic products is analyzed. The influence followed by metal element loading on the structure and properties of CuO-based materials by MWHS process is further discussed. Then this review summarizes the research progress of graphene-CuO and metal oxide-CuO composites prepared by MWHS process in recent years.