Biochar is a solid by-product of thermochemical conversion of biomass to bio-oil and syngas. It has a carbonaceous skeleton, a small amount of heteroatom functional groups, mineral matter, and water. ...Biochar’s unique physicochemical structures lead to many valuable properties of important technological applications, including its sorption capacity. Indeed, biochar’s wide range of applications include carbon sequestration, reduction in greenhouse gas emissions, waste management, renewable energy generation, soil amendment, and environmental remediation. Aside from these applications, new scientific insights and technological concepts have continued to emerge in the last decade. Consequently, a systematic update of current knowledge regarding the complex nature of biochar, the scientific and technological impacts, and operational costs of different activation strategies are highly desirable for transforming biochar applications into industrial scales. This communication presents a comprehensive review of physical activation/modification strategies and their effects on the physicochemical properties of biochar and its applications in environment-related fields. Physical activation applied to the activation of biochar is discussed under three different categories: I) gaseous modification by steam, carbon dioxide, air, or ozone; II) thermal modification by conventional heating and microwave irradiation; and III) recently developed modification methods using ultrasound waves, plasma, and electrochemical methods. The activation results are discussed in terms of different physicochemical properties of biochar, such as surface area; micropore, mesopore, and total pore volume; surface functionality; burn-off; ash content; organic compound content; polarity; and aromaticity index. Due to the rapid increase in the application of biochar as adsorbents, the synergistic and antagonistic effects of activation processes on the desired application are also covered.
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•An aminated GO for CO2 adsorption was prepared by a novel ultrasound-enhanced amine-functionalization method.•The ultrasound irradiation was very effective in the interaction between ...the amine and the oxygen-containing groups of GO.•The thermal resistance property of aminated GO makes it ideal candidate for CO2 adsorption from flue gas.•The aminated GO exhibited a better adsorption capacity of 1.2 mmol g−1 of adsorbent in the flue gas temperature (338 K).
The present study discusses a novel ultrasound promoted amination technique to functionalize graphene oxide (GO) for CO2 adsorption. Graphene oxide was synthesized following the modified Hummer’s method. The developed functionalization technique integrates the advantages of low-frequency ultrasonic physical activation with the chemical functionalization using tetraethylenepentamine (TEPA). Acoustic treatment exfoliates the clusters of graphene oxide and enhances the surface area for the subsequent amine functionalization and CO2 adsorption. Changes in textural properties, surface functionalities, thermal stability, and elemental compositions were examined before and after activation of graphene oxide. The characterization results revealed substantial increment of N content, from 0.08 in pristine to 4.84% in functionalized GO and the subsequent reduction in surface area from 289 to 198 m2/g in the functionalized GO, indicating attachment of TEPA to GO structure. CO2 adsorption experiments were conducted under diluted CO2 with the partial pressure of 0.10 atm. at 338 K and the results revealed that ultrasonic-TEPA activated GO possessed enhanced adsorption capacity of 1.2 mmol g−1 over pristine GO. While pristine GO could only achieve the maximum adsorption capacity of 0.3 mmol g−1 at 303 K. Besides, the sonochemically modified adsorbent showed stable cyclic adsorption-regeneration performance with only 1% reduction in adsorption capacity after 10 cycles. Finally, the effectiveness of the developed physicochemical activation technique was determined by comparing its adsorption capacity with the adsorbents found from literature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Oxide perovskites have emerged as an important class of materials with important applications in many technological areas, particularly thermocatalysis, electrocatalysis, photocatalysis, and energy ...storage. However, their implementation faces numerous challenges that are familiar to the chemist and materials scientist. The present work surveys the state-of-the-art by integrating these two viewpoints, focusing on the critical role that defect engineering plays in the design, fabrication, modification, and application of these materials. An extensive review of experimental and simulation studies of the synthesis and performance of oxide perovskites and devices containing these materials is coupled with exposition of the fundamental and applied aspects of defect equilibria. The aim of this approach is to elucidate how these issues can be integrated in order to shed light on the interpretation of the data and what trajectories are suggested by them. This critical examination has revealed a number of areas in which the review can provide a greater understanding. These include considerations of (1) the nature and formation of solid solutions, (2) site filling and stoichiometry, (3) the rationale for the design of defective oxide perovskites, and (4) the complex mechanisms of charge compensation and charge transfer. The review concludes with some proposed strategies to address the challenges in the future development of oxide perovskites and their applications.
The present work provides a critical review of the science and technological state-of-the-art of defect engineering applied to oxide perovskites in thermocatalytic, electrocatalytic, photocatalytic, and energy-storage applications.
•Micro-bubbles were mechanistically analyzed/characterized using mathematical modeling.•Their equilibrium radius, oscillation velocity, hot spot conditions were investigated.•Acoustic streaming, ...fluid flow pattern, turbulence were analyzed using 3D CFD.•Total volume fraction of micro-bubbles was also analyzed by 3D CFD.•Fluid flow pattern and acoustic streaming were practically analyzed using PIV.
This paper aims at investigating the influence of ultrasound power amplitude on liquid behaviour in a low-frequency (24kHz) sono-reactor. Three types of analysis were employed: (i) mechanical analysis of micro-bubbles formation and their activities/characteristics using mathematical modelling. (ii) Numerical analysis of acoustic streaming, fluid flow pattern, volume fraction of micro-bubbles and turbulence using 3D CFD simulation. (iii) Practical analysis of fluid flow pattern and acoustic streaming under ultrasound irradiation using Particle Image Velocimetry (PIV). In mathematical modelling, a lone micro bubble generated under power ultrasound irradiation was mechanistically analysed. Its characteristics were illustrated as a function of bubble radius, internal temperature and pressure (hot spot conditions) and oscillation (pulsation) velocity. The results showed that ultrasound power significantly affected the conditions of hotspots and bubbles oscillation velocity. From the CFD results, it was observed that the total volume of the micro-bubbles increased by about 4.95% with each 100W-increase in power amplitude. Furthermore, velocity of acoustic streaming increased from 29 to 119cm/s as power increased, which was in good agreement with the PIV analysis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The present study examined the effect of pyrolysis temperature on the physicochemical properties of biochar, activation process and carbon capture. Two different categories of biochars were ...synthesized from herbaceous (miscanthus and switchgrass) and agro-industrial (corn stover and sugarcane bagasse) feedstock under four different pyrolysis temperatures −500, 600, 700, and 800°C. The synthesized biochars underwent sono-amination activation comprising low-frequency acoustic treatment followed by amine functionalization to prepare adsorbents for CO2 capture. The highest increment (200%) of CO2 capture capacity was observed for sono-aminated samples prepared at 600 and 700°C (maximum improvement for miscanthus), while biochars synthesized at 500 and 800°C demonstrated comparatively lesser increment in adsorption capacities that falls in the range of 115–151 and 127–159%, respectively compared to 600 and 700°C. The elevated pyrolysis temperature (particularly 600 and 700°C) resulted in increased %C and %ash contents and reduced %N contents with enhancement of micro surface area and pore volume. Thus, the superior adsorption capacity of miscanthus (at 600 and 700°C) can be attributed to their large surface areas (303–325 m2/g), high carbon contents (82–84%), and low ash contents (4–5%), as well as %N contents after sono-amination that was twice that of raw char.
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•Ultrasound irradiation was applied for physical treatment of biochar at room temperature.•The sono-treated biochar was functionalized with tetraethylenepentamine (TEPA).•The modified ...biochar demonstrated a great potential for CO2 capture.
This paper describes a two-stage biochar activation process for CO2 capture, which includes acoustic treatment and amination. Contrarily to traditional carbon activation at temperatures above 700 °C, both stages of the current process are conducted at or near room temperature. It is known that CO2 can be fixed on the edge carbons of polycyclic aromatics hydrocarbons (PAHs) through thermal and reductive photo-carboxylation. Our previous work on biochar suggested that carbon of CO2 could be chemically fixed on biochar through acoustic or photochemical treatment of biochar in water/CO2 systems under ambient conditions. Separately, the graphene oxide (GO) literature reveals that carboxylic acids, epoxy and hydroxyl groups on biochar surface often serve as the active sites for converting GO to a new family of chemicals; amines are commonly grafted on these groups in the functionalization. Biochar has graphite and graphitic oxide clusters that consist of the oxygen functional groups mentioned above. These oxygen functionalities can be utilized for CO2 adsorption when functionalized with amine. Thus, the present study focuses on maximizing the CO2 capture capacity by manipulating the physicochemical structure of a pinewood-derived biochar. In this two-stage process, 30 s sonication at ambient temperature was applied to physically activate biochar prior to functionalization. Low-frequency ultrasound irradiation exfoliates and breaks apart the irregular graphitic layers of biochar, and creates new/opens the blocked microspores, thus enhancing the biochar’s porosity and permeability that are the keys in functionalization and subsequent CO2 capture. The sono-modified biochar was then functionalized with tetraethylenepentamine (TEPA) in the presence of two activating agents. The changes in surface characteristics, functional groups, graphene-like structure, and functionalization using activating agents were examined in detail and the capacity of the final products in CO2 removal was tested. The experimental results revealed that CO2 capture capacity, from a flow containing 10 and 15 vol% CO2, was almost 7 and 9 times higher, respectively, for ultrasound-treated amine-activated biochar, compared to raw biochar. The optimum capacity was 2.79 mmol/g at 70 °C and 0.15 atm CO2 partial pressure. Cyclic adsorption and desorption tests revealed that the CO2 capture capacity decreased 44% after 15 cycles.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The present study discusses a novel biochar activation technique consisting of physical modification using low frequency ultrasound and chemical functionalization with individual amines and their ...blended mixtures in the presence of two activating agents. Acoustic treatment under ultrasonic irradiation exfoliates the biochar’s graphitic clusters, creates new micropores, opens the blocked pores, and enhances the functionalization efficiency. In a subsequent chemical modification step, functionalization with amine moieties further boosts the adsorption capacity. Therefore, the effect of five different amines was investigated on ultrasono-activated biochar (i) monoethanolamine (MEA, 1°), (ii) piperazine (PZ, 2°), (iii) diethanolamine (DEA, 2°), (iv) tetraethylenepentamine (TEPA, 1° and 2°), and (v) polyethylenimine (PEI, 1°, 2°, and 3°) and several binary and ternary mixtures (1) MEA–TEPA, (2) DEA–TEPA, (3) DEA–PEI, (4) TEPA–PEI, and (5) DEA–TEPA–PEI with the activating agents N-(3-(dimethylamino)propyl-N′-ethylcarbodiimide hydrochloride (EDC)–hydroxybenzotriazole (HOBt) or potassium hydroxide (KOH). The results revealed that ultrasonically treating biochar samples for 30 s, followed by chemical activation with either EDC–HOBt–TEPA–MEA or KOH–MEA gave materials possessing intensified adsorption capacities of 1.91 and 1.62 mmol/g, respectively, at 0.10 atm CO2 partial pressure and 70 °C, compared to raw biochar (0.3 mmol/g).
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IJS, KILJ, NUK, PNG, UL, UM
•Analysis of ultrasound waves propagation in gas-liquid media using CFD simulation.•Analysis of mass transfer intensification under ultrasound irradiation.•Analysis of the effects of acoustic ...streaming, fluid flow pattern, turbulence on KLa.
This paper aims at investigating the influence of acoustic streaming induced by low-frequency (24kHz) ultrasound irradiation on mass transfer in a two-phase system. The main objective is to discuss the possible mass transfer improvements under ultrasound irradiation. Three analyses were conducted: i) experimental analysis of mass transfer under ultrasound irradiation; ii) comparative analysis between the results of the ultrasound assisted mass transfer with that obtained from mechanically stirring; and iii) computational analysis of the systems using 3D CFD simulation. In the experimental part, the interactive effects of liquid rheological properties, ultrasound power and superficial gas velocity on mass transfer were investigated in two different sonicators. The results were then compared with that of mechanical stirring. In the computational part, the results were illustrated as a function of acoustic streaming behaviour, fluid flow pattern, gas/liquid volume fraction and turbulence in the two-phase system and finally the mass transfer coefficient was specified. It was found that additional turbulence created by ultrasound played the most important role on intensifying the mass transfer phenomena compared to that in stirred vessel. Furthermore, long residence time which depends on geometrical parameters is another key for mass transfer. The results obtained in the present study would help researchers understand the role of ultrasound as an energy source and acoustic streaming as one of the most important of ultrasound waves on intensifying gas-liquid mass transfer in a two-phase system and can be a breakthrough in the design procedure as no similar studies were found in the existing literature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The use of hybrid advanced oxidation processes（AOPs） for the removal of pollutants from industrial effluents has been extensively studied in recent literature. The aim of this study is to compare the ...performance of the photo,Fenton, photo-Fenton and ozone–photo–Fenton processes in terms of color removal and chemical oxygen demand（COD） removal of distillery industrial effluent together with the associated electrical energy per order. It was observed from the experimental results that the O3/UV/Fe^2＋/H2O2 process yielded a 100% color and95.50% COD removals with electrical energy per order of 0.015 kW·h·m^-3 compared to all other combinations of the AOPs. The effects of various operating parameters such as H2O2 and Fe^2＋ concentration, effluent pH, COD concentration and UV power on the removal of color, COD and electrical energy per order for the ozone–photo–Fenton process was critically studied and reported. The color and COD removals were analyzed using a UV/Vis spectrometer and closed reflux method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Comparison of UV, H2O2, Fe2+, UV/H2O2, UV/Fe2+, Fe2+/H2O2 and UV/Fe2+/H2O2 processes for the removal of percentage color, COD and electrical energy per order from the effluent distillery industry. ...The results showed that, UV/Fe2+/H2O2 process yield higher percentage color and COD removal with low electrical energy per order than UV, UV/H2O2, UV/Fe2+ process. To obtain the UV/Fe2+/H2O2 process performance by operating various parameters on the percentage color and COD removal using response surface methodology. A Regression quadratic model describing the percentage color and COD removal efficiency of UV/Fe2+/H2O2 process were developed and validate by analysis of variance. Experimental results showed that, UV/Fe2+/H2O2 process can effectively reduced 96.50% of color and 84.40% of COD removal of the distillery industry wastewater under the optimum conditions such as Fe2+–1.50mM, H2O2–200mM, COD–1500ppm and pH–3.2, respectively. Result concluded that, UV/Fe2+/H2O2 process can be used effectively for the treatment of real industrial effluent.
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•Comparison of UV, H2O2, Fe2+, UV/H2O2, UV/Fe2+, Fe2+/H2O2 and UV/Fe2+/H2O2 process on the removal of pollutant with electrical energy per order.•UV/Fe2+/H2O2 process has yielded higher pollutant removal with low electrical energy per order.•RSM was used to investigate the effect of operating parameters to achieve the maximum removal of pollutant with requirement of low electrical energy per order.•The quadratic regression model was developed for the response and the model well matched with actual value.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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