Preparation and Characterization of Activated Carbon from Sesame Seed Shells by Microwave and Conventional Heating with Zinc Chloride Activation

The preparation of activated carbon from sesame shells as raw precursor was investigated in the study by sequentially applying microwave and conventional heating methods assisted by zinc chloride activation. The optimizisation of experimental parameters including microwave power, microwave treatment time, conventional activation time, conventional activation temperature and zinc chloride concentration ratio for the microwave and conventional heating method was performed. The characterization of the prepared activated carbon was done by thermogravimetric and differential thermal measurements, infrared spectroscopy, scanning electron microscopy and specific surface area analyses. The maximum surface area of 1254?m²/g for the prepared activated carbon was obtained at a microwave power of 750?W, a microwave treatment time of 20?min, an activation time of 45?min, an activation temperature of 500°C and zinc chloride concentration ratio of 1:1. Methylene blue and iodine adsorption capacities for the prepared activated carbon were 103 and 1199?mg/g, respectively.     

Characterization of Microwave and Conventional Heating on the Pyrolysis of Pistachio Shells for the Adsorption of Methylene Blue and Iodine

The production of activated carbon was investigated using the sequential combination of microwave and conventional heating of pistachio shells as the raw precursor with zinc chloride. Several techniques such as thermogravimetric and differential thermal analyses, infrared spectroscopy, scanning electron microscopy, and specific surface area analyses were performed to characterize the samples. The highest specific surface area value for the activated carbon prepared at a microwave power of 200?W with microwave time of 20?min, and flow rate of 50?mL?min^?1 was 1468?m²?g^?1. The methylene blue and iodine adsorption capacities were 331 and 1276?mg?g^?1, respectively. The results were compared to those obtained using physical and chemical activation methods and showed that the sequential combination of microwave and conventional heating reasonably influenced the micropore surface area of the samples as well as the specific surface area.     

Microwave assisted preparation of efficient activated carbon from grapevine rhytidome for the removal of methyl violet from aqueous solution

Grapevine rhytidome (the outer layer of bark on trunk), as an abundant and low-cost precursor, was used to prepare granular activated carbon with high surface area for the removal of methyl violet from aqueous solution. Microwave heating source was used to reduce the treatment time and energy consumption. To optimize the preparation, the effects of the different parameters, such as phosphoric acid concentration, acid/precursor weight ratio, impregnation time, microwave power, radiation time, and oven heating time on the ability of the samples for removal of methyl violet were studied. The obtained activated carbon was characterized by N₂ adsorption/desorption, SAXS, TEM and SEM methods. The adsorption of methyl violet onto the activated carbon was studied from both equilibrium and kinetic point of view and the results were compared with the commercial granular activated carbon. The rate of adsorption onto the prepared activated carbon was faster than commercial activated carbon. Different kinetic models were used to analyze the experimental kinetic data. The obtained activated carbon showed higher adsorption capacity (more than twice) for the adsorption of methyl violet in comparison with the commercial one. The equilibrium data were analyzed using different isotherm models. Adsorption was found to be maximum in the pH range 7-9.     

Fe‐, Co‐, and Ni‐Loaded Porous Activated Carbon Balls as Lightweight Microwave Absorbents

Porous activated carbon ball (PACB) composites impregnated with iron, cobalt, nickel and/or their oxides were synthesized through a wet chemistry method involving PACBs as the carrier to load Fe³⁺, Co²⁺, and Ni²⁺ ions and a subsequent carbothermal reduction at different annealing temperatures. The results show that the pyrolysis products of nitrates and/or the products from the carbothermal reduction are embedded in the pores of the PACBs, with different distributions, resulting in different crystalline phases. The as‐prepared PACB composites possessed high specific surface areas of 791.2–901.5 m² g^?1 and low densities of 1.1–1.3 g cm^?3. Minimum reflection loss (RL) values of ?50.1, ?20.6, and ?20.4 dB were achieved for Fe–PACB (annealed at 500 °C), Co–PACB (annealed at 800 °C), and Ni–PACB (annealed at 800 °C) composites, respectively. Moreover, the influence of the amount of the magnetic components in the PACB composites on the microwave‐absorbing performances was investigated, further confirming that the dielectric loss was the primary contributor to microwave absorption.     

Dissolution of sintered thorium dioxide in phosphoric acid using autoclave and microwave methods with detection by gamma spectrometry

A quantitative and fast method of dissolution of refractory thoria (ThO₂) was developed for the determination of thorium (Th) in a given sample. The dissolution of sintered ThO₂ powder, microspheres and pellets using 88% phosphoric acid was investigated. The conditions of quantitative dissolution of ThO₂ microspheres were optimized by conventional heating in autoclave and also by microwave heating. 100 mg of sintered ThO₂ microspheres were dissolved in 8 g of phosphoric acid in an autoclave, and heating at 170 °C for 3 h, in comparison to 5 g of phosphoric acid by microwave heating (375 W) at 220 °C for 1 h. Dissolution studies on the powder form of sintered ThO₂ were also performed. 1 g of sintered ThO₂ powder could be dissolved in 6.5 g of phosphoric acid in autoclave heating at 170 °C for 1 h. Strong complexing of (PO₄)³⁻ with Th⁴⁺ may be the influencing factor for quantitative dissolution of ThO₂.     

Structural and surface heterogeneity of phosphorus-containing polyimide-derived carbons: effect of heat treatment temperature

Phosphorus-containing carbons have been obtained by carbonization of porous copolymer of 4,4′-bis(maleimidodiphenyl)methane (50 mol%) and divinylbenzene (50 mol%) in presence of phosphoric acid at temperatures 400–1000 °C. Porous structure was analyzed by nitrogen adsorption isotherms while surface chemistry was investigated by potentiometric titration method. It has been shown that carbons obtained at 500–1000 °C are micro-mesoporous with pore sizes of 1–1.1, 2–3 and 5.4 nm. The most developed porosity was achieved at 600 °C reaching BET surface area 890 m²/g and total pore volume 0.45 cm³/g. Carbons obtained by carbonization of polyimide precursor in presence of phosphoric acid showed acidic character with 30–40 % of phosphate surface groups. Maximum total amount of acidic surface groups was achieved at 800 °C reaching 3.2 mmol/g. Assignment of strongly acidic surface groups to phosphates was corroborated by pK value, phosphorus content and thermal gravimetric analysis.     

Conversion of teak wood waste into microwave-irradiated activated carbon for cationic methylene blue dye removal: Optimization and batch studies

The objective of this study is to find optimum preparation conditions in converting teak wood waste into activated carbon (TWAC) and to evaluate its performance in adsorbing cationic dye of methylene blue (MB). TWAC was produced via physiochemical activation (potassium hydroxide, KOH chemical treatment, and carbon dioxide, CO₂ gasification) and heated through microwave irradiation technique. With the aid of response surface methodology (RSM), optimized TWAC was successfully synthesized at radiation power, radiation time, and impregnation ratio (IR) of 366 W, 5.30 min, and 1.15 g/g, respectively. These preparation conditions produced TWAC with MB adsorption uptakes of 66.69 mg/g and a yield of 38.23%. Characteristics of TWAC in terms of BET surface area, mesopores surface area, total pore volume, and average pore diameter were determined to be 1345.25 m²/g, 878.63 m²/g, 0.6140 cm³/g, and 2.85 nm, respectively. Isotherm studies divulged that the MB-TWAC adsorption system followed the Langmuir model with a maximum monolayer adsorption capacity of 567.52 mg/g. In terms of kinetic studies, this adsorption system fit pseudo-second order model the best whereas Boyd plot confirmed that the adsorption process was controlled by the film diffusion mechanism. Thermodynamic parameters of enthalpy change, ΔH°, entropy change, ΔS°, Gibbs free energy, ΔG° and Arrhenius activation energy, E_a were calculated to be ?4.06 kJ/mol, 0.06 kJ/mol.K, –22.69 kJ/mol and 16.03 kJ/mol, respectively. The activation and microwave heating methods employed succeeded to produce TWAC with excellent adsorption performance in removing MB dye. TWAC was also successfully regenerated for 5 cycles via microwave heating technique.     

Preparation and characterization of activated carbon from pine cone by microwave-induced ZnCl2 activation and its effects on the adsorption of methylene blue

In this work, activated carbon prepared from pine cone (PCAC) with ZnCl₂ as an activation agent under microwave radiation was investigated. The activation step was performed at the microwave input power of 400 W and radiation time of 5 min. The properties of activated carbon were characterized by N₂ adsorption Brunauer–Emmett–Teller (BET), scanning electron microscopy and Fourier transform infrared spectroscopy. Results showed that the BET surface area, Langmuir surface area, and total pore volume of PCAC were 939, 1,486 m²/g and 0.172 cm³/g, respectively. Adsorption capacity was demonstrated by the iodine numbers. The adsorptive property of PCAC was tested using methylene blue dye. Equilibrium data was best fitted by the Langmuir isotherm model, showing a monolayer adsorption capacity of 60.97 mg/g. The pseudo-first- and pseudo-second-order kinetic models were examined to evaluate the kinetic data, and the rate constants were calculated. Adsorption of the dyes followed pseudo-first order kinetics. Thermodynamic parameters such as free energy, enthalpy and entropy of dye adsorption were obtained.     

Effects of activation conditions on the structural and adsorption characteristics of pinecones derived activated carbons

This study was conducted to understand and optimize the activation process for the production of a low-cost activated carbon (AC) using a renewable and plentiful biomass waste, pinecones. This was achieved by tracking the changes in porous structure, surface chemistry and adsorption properties of the AC produced using different activating agents, activation temperatures, holding times and heating rates. Generally, produced ACs were predominantly microporous with small external surface area and were different in terms of H/C and O/C ratios. Study of Pb²⁺ cations adsorption on these samples proved the high affinity of the pinecones derived ACs to this cation. The best adsorption behaviour was recognized in sample prepared by impregnation with H₃PO₄ at weight ratio of 2, then heating at 400?°C for 2?h at 5?°C/min heating rate. This sample possessed the highest BET surface area (1335 m²/g). The adsorption process obeyed the pseudo-first-order and Freundlich model slightly better than the pseudo-second-order kinetics and Langmuir model. The high Langmuir maximum adsorption capacity of 418?mg/g supports the applicability of the produced AC for the removal of Pb²⁺ cations from wastewater.     

Adsorption of cationic methylene blue dye using microwave-assisted activated carbon derived from acacia wood: Optimization and batch studies

This study assesses the performance of optimized acacia wood-based activated carbon (AWAC) as an adsorbent for methylene blue (MB) dye removal in aqueous solution. AWAC was prepared via a physicochemical activation process that consists of potassium hydroxide (KOH) treatment, followed by carbon dioxide (CO₂) gasification under microwave heating. By using response surface methodology (RSM), the optimum preparation conditions of radiation power, radiation time, and KOH-impregnation ratio (IR) were determined to be 360 W, 4.50 min, and 0.90 g/g respectively, which resulted in 81.20 mg/g of MB dye removal and 27.96% of AWAC’s yield. Radiation power and IR had a major effect on MB dye removal while radiation power and radiation time caused the greatest impact on AWAC’s yield. BET surface area, mesopore surface area, and pore volume of optimized AWAC were found to be 1045.56 m²/g, 689.77 m²/g, and 0.54 cm³/g, respectively. Adsorption of MB onto AWAC followed Langmuir and pseudo-second order for isotherm and kinetic studies respectively, with a Langmuir monolayer adsorption capacity of 338.29 mg/g. Mechanism studies revealed that the adsorption process was controlled by film diffusion mechanism and indicated to be thermodynamically exothermic in nature.     

微波辐射活性炭负载磷钨酸催化合成季戊四醇双缩酮(醛)

在微波辐射下，以活性炭负载磷钨酸为催化剂，不用溶剂，合成了8种季戊四醇双缩酮（醛），以环己酮与季戊四缩的缩合为模型反应进行优化，其优化反应条件为：季戊四醇2．0g，催化剂0．3g，环己酮4．0mL，微波输出功率600W，辐射时间3min，产率达95．4％，该条件下的反应速度是常规加热反应速度的30倍，所得产物经元素分析，IR和1H NMR表征。     

High temperature all solid state supercapacitor based on multi-walled carbon nanotubes and poly[2,5 benzimidazole]

Supercapacitor containing multi-walled carbon nanotubes (MWCNT) as the electrode material and phosphoric acid-doped poly[2,5 benzimidazole] (ABPBI) as the solid electrolyte and separator membrane has been investigated in a wide temperature range. Supercapacitors with different solid electrolyte concentrations have been fabricated and evaluated for their electrochemical performance. Specific capacitance of supercapacitors at room temperature was found to increase after the first heating cycle. Supercapacitor containing 10?wt.% of solid electrolyte in the electrode shows higher specific capacitance than the supercapacitor with liquid electrolyte. Cyclic voltammetry analysis of supercapacitors indicates high rate capability. The linear increase in the specific capacitance with temperature implies that capacitance is predominantly due to electric double layer. Electrochemical impedance analysis indicates that the mass capacitance and Warburg parameter increase with temperature, while solution resistance and leakage resistance decrease with temperature. The complex capacitance of the supercapacitors shows that both real and loss capacitances increase with temperature. The phase angle of supercapacitors is found to be around 85.2?±?1° at room temperature and it decreases with temperature. Galvanostatic charge–discharge cycling exhibits almost constant specific capacitance of 28?F?g^?1 at room temperature. However, it increases sharply and then attains stable value of 52?F?g^?1 during cycling at 100?°C. The increase in specific capacitance has been attributed to increase in surface area of the carbon nanotube (CNT), due to activation by phosphoric acid and diffusion of free phosphoric acid into the central canal of MWCNT.     

微波辐射在制备竹节活性炭中的应用研究

研究了以竹节废料为原料，采用微波辐射氯化锌法制备优质活性炭的可行性．探讨了微波功率．活化时间及氯化锌浓度对产品各项指标的影响．得到了微波辐射氯化锌法制备活性炭的最佳工艺：微波功率350W、活化时间5min、氯化锌浓度40%．用此工艺制得的活性炭碘吸附值1088．4mg／g、亚甲基蓝脱色力22．0ml/0．1g．得率39．2％．该工艺所需活化时间为传统方法的1／36，产品活性炭亚甲基蓝脱色力为国家一级标准的1．83倍(GB/T13496.10-1999)．微波辐射法所制活性炭比传统方法所制活性炭具有更加发达的孔隙结构，且孔隙的分布更加均匀．     

Preparation of Corn Stalk-Walnut Shell Mix-based Activated Carbon and Its Adsorption of Malachite Green

The mix-based activated carbon derived from corn stalk and walnut shell was prepared by chemical activation method using phosphoric acid as the activator. The optimized conditions for preparation were obtained by the orthogonal experiment, the characterizations of the activated carbon were performed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy(FTIR), Boehm's titration method and nitrogen adsorption. For the prepared mix-based activated carbon, the highest iodine number, methylene blue number and BET surface area are 720.5 mg/g, 195.0 mg/g and 1187 m²/g, respectively, and the pores are mainly mesopores. The mix-based activated carbon shows the higher adsorption capacity for malachite green than the raw materials, the activated carbons prepared only from corn stalk or walnut shell and the commercial activated carbon. The kinetics and thermodynamics of the adsorption can be satisfactorily described by the pseudo-second-order kinetic model and the Langmuir isotherm model, separately.     

Optimization of sulfamethazine sodium adsorption onto activated carbon-based Salix psammophila: investigation of adsorption behavior and mechanism

A study on the adsorption of sulfamethazine sodium (SMS) from aqueous solution onto the activated carbon (AC)-based Salix psammophila (SP) by phosphoric acid activation was conducted. The central composite design under response surface methodology was employed for the removal of SMS and the process parameters were optimized. Influence of adsorbent dose, initial concentration of SMS, contact time and solution pH on the adsorption capacity of AC was investigated. The optimum adsorption conditions were obtained using adsorbent dosage of 0.54?g/L, initial concentration of 322?mg/L, contact time of 8?hours, pH value of 4.04. Kinetic studies showed the adsorption followed a pseudo-second-order model and Elovich model. The experimental equilibrium data were fitted Koble-Corrigan model and Freundlich model well and the maximum monolayer adsorption capacity of AC calculated by Langmuir model was 338.58?mg/g at 25?°C. In addition, AC was characterized by the SEM–EDS, BET, FITR and point of zero charge (pH_pzc). The mechanisms of SMS sorption onto AC were explored. Desorption and regeneration tests were carried out to evaluate the feasibility of reusing the AC. This study indicated the AC prepared from SP was an excellent adsorbent with the low cost and high performance.     

A New Approach for Controlling Mesoporosity in Activated Carbon by the Consecutive Process of Air Oxidation,Thermal Destruction of Surface Functional Groups,and Carbon Activation (the OTA Method)

A new and simple method, based entirely on a physical approach, was proposed to produce activated carbon from longan fruit seed with controlled mesoporosity. This method, referred to as the OTA, consisted of three consecutive steps of (1) air oxidation of initial microporous activated carbon of about 30% char burn-off to introduce oxygen surface functional groups, (2) the thermal destruction of the functional groups by heating the oxidized carbon in a nitrogen atmosphere at a high temperature to increase the surface reactivity due to increased surface defects by bond disruption, and (3) the final reactivation of the resulting carbon in carbon dioxide. The formation of mesopores was achieved through the enlargement of the original micropores after heat treatment via the CO₂ gasification, and at the same time new micropores were also produced, resulting in a larger increase in the percentage of mesopore volume and the total specific surface area, in comparison with the production of activated carbon by the conventional two-step activation method using the same activation time and temperature. For the activation temperatures of 850 and 900 °C and the activation time of up to 240 min, it was found that the porous properties of activated carbon increased with the increase in activation time and temperature for both preparation methods. A maximum volume of mesopores of 0.474 cm³/g, which accounts for 44.1% of the total pore volume, and a maximum BET surface area of 1773 m²/g was achieved using three cycles of the OTA method at the activation temperature of 850 °C and 60 min activation time for each preparation cycle. The two-step activation method yielded activated carbon with a maximum mesopore volume of 0.270 cm³/g (33.0% of total pore volume) and surface area of 1499 m²/g when the activation temperature of 900 °C and a comparable activation time of 240 min were employed. Production of activated carbon by the OTA method is superior to the two-step activation method for better and more precise control of mesopore development.     

Microwave-activated carbon dioxide reforming of propane over Ni/TiO<Subscript>2</Subscript> catalysts

The use of microwave activation in Ni/TiO₂-catalyzed carbon dioxide reforming of propane increases the catalytic activity and significantly reduces the coke formation in comparison with conventional thermal heating. During microwave activated reaction, C₂—C₃ olefins were formed, apart from CO and H₂, and the selectivity to olefins reached 6%. It was suggested that exposure to microwave radiation may induce local high-temperature heating of catalytically active phases and catalyst sites, which is not inherent in conventional heating. According to X-ray absorption spectroscopy (XAS = XANES + EXAFS), unlike conventional thermal heating in a hydrogen flow, on exposure to microwave radiation, the Ni²⁺ cations are partly reduced to Ni⁰.     

Adsorption of Cu(II) ions from aqueous solution by hazelnut husk activated carbon prepared with potassium acetate

Hazelnut husk (HH), an agricultural waste, was converted to carbonaceous material by chemical activation using potassium acetate. The produced activated carbon (KAHHAC) was characterized by FTIR, SEM, N₂ adsorption–desorption experiments, CHN elemental analysis, and determination of moisture, ash, and point of zero charge. KAHHAC was used for the batch adsorption of Cu(II) ions from aqueous solutions. Optimum pH and contact time were found to be 5.0 and 240 minutes, respectively. The adsorption equilibrium data were described well by the Langmuir equation providing 105.3?mg?g^?1 Cu(II) adsorption capacity. The pseudo-second-order model successfully described the kinetic of Cu(II) adsorption by KAHHAC. The adsorbed Cu(II) onto KAHHAC was completely desorbed by 0.5?M nitric acid. In conclusion, HH activated carbon (AC) produced by the potassium acetate activation method is a very useful and efficient sorbent material for the removal of Cu(II) from aqueous solution.     

Adsorption of uranium from crude phosphoric acid using activated carbon

The adsorption of uranium from crude phosphoric acid has been investigated using conventional activated carbons. It was found that treatment with nitric acid oxidized the surface of activated carbon and significantly increased the adsorption capacity for uranium in acidic solutions. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated. Equilibrium data were fitted to a simplified Langmuir and Freundlich isotherms for the oxidized samples which indicate that the uranium adsorption onto the activated carbon fitted well with Langmuir isotherm than Freundlich isotherm. Equilibrium studies evaluate the theoretical capacity of activated carbon to be 45.24 g kg^?1.