Microwave-assisted KOH Activation Research Articles

Fabrication of developed porous carbon derived from bluecoke powder by microwave-assisted KOH activation for simulative organic wastewater treatment

Bluecoke powder (BC) was used as a precursor to prepare porous carbon (MKBC) by microwave-assisted KOH activation. The physical and chemical properties of MKBC were investigated by SEM, FT-IR, Raman, and its adsorption performance for simulative organic wastewater was detected by ultraviolet spectrum analyses. Results indicated that the surface morphology of BC was changed by microwave-assisted KOH activation, resulting in abundant macropores and micropore structures on MKBC. The high porosity of the developed meso- and micropore structures on MKBC enhanced the adsorption capacity, with the maximum Langmuir adsorption capacity (qm) of 307.692 mg/g. The kinetics were more consistent with the pseudo-first-order model when the methylene blue concentration was 50 mg/L and with the Elovich model as the concentration further increased (150 mg/L). Moreover, MKBC showed high affinity toward methylene blue at low concentrations, and the removal rate of methylene blue was more than 99% in less than 1 h. The regeneration and applicability results showed that MKBC had significant stability and effectiveness, and had a certain removal effect on malachite green, rhodamine B, p-nitrophenol, and tetracycline in wastewater, in which p-nitrophenol was the best. Efficient and low-cost MKBC could play an important role in the treatment of organic wastewater and provide a new value-added utilization for BC.

Preparation of Straw Porous Biochars by Microwave-Assisted KOH Activation for Removal of Gaseous H2S

Two types of straw porous biochars were prepared from agricultural waste (i.e., rice straw and wheat straw) using microwave-assisted KOH activation to eliminate H2S in the gas phase. Influences of sorption temperatures and KOH/biochar mass ratios on the performance of the adsorbent for H2S removal were studied. Several characterization methods were used to analyze the changes in physical structures and the changes of chemical sorption sites of the samples before/after activation and H2S removal experiment. H2S adsorbing kinetics was explored, and the sorption capacities for gaseous Hg0 of the spent adsorbents were also tested. The results exhibited that the physical structures of straw porous biochars were evidently improved, and the contents of the oxygen-containing functional group were also raised via the activation of microwave-assisted KOH. The largest specific surface areas of rice straw/wheat straw porous biochars are, respectively, up to 1999.96 m2/g (WKRS4) and 877.16 m2/g (WKWS4), resulting in the best performance for eliminating H2S. The equilibrium adsorption capacities of WKRS4/WKWS4 to H2S are 57.91 and 61.47 mg/g, respectively. Both temperature and KOH/biochar mass ratio achieve dual effects on H2S sorption. In the sorption processes of H2S over two types of porous materials, both of the rate-determining steps are the external mass transfers. The deactivated porous biochars after adsorbing H2S showed good capturing capabilities for Hg0 in the gas phase.

Parametric Study on Microwave-Assisted Pyrolysis Combined KOH Activation of Oil Palm Male Flowers Derived Nanoporous Carbons.

Oil palm male flowers (PMFs), an abundant agricultural waste from oil palm plantation in Thailand, have been utilized as an alternative precursor to develop nanoporous carbons (NPCs) via microwave-assisted pyrolysis combined potassium hydroxide (KOH) activation. The influences of relevant processing variables, such as activating agent ratio, microwave power, and activation time on the specific pore characteristics, surface morphology, and surface chemistry of PMFs derived nanoporous carbons (PMFCs) have been investigated to explore the optimum preparation condition. The optimum condition under a microwave radiation power of 700 W, activation holding time of 6 min, and activating agent ratio of 2:1 obtained the PMFC with the highest Brunauer–Emmett–Teller (BET) surface area and total pore volume approximately of 991 m2/g and 0.49 cm3/g, composed of a carbon content of 74.56%. Meanwhile, PMFCs have a highly microporous structure of about 71.12%. Moreover, activating agent ratio and microwave radiation power indicated a significant influence on the surface characteristics of PMFCs. This study revealed the potential of oil palm male flowers for the NPCs’ production via microwave-assisted KOH activation with a short operating-time condition.

Microwave-assisted KOH activation from lignin into hierarchically porous carbon with super high specific surface area by utilizing the dual roles of inorganic salts: Microwave absorber and porogen

Searching an appropriate biomass that is capable of absorbing microwave energy is significant to realize its rapid microwave-assisted conversion into porous carbons (PCs). Herein, the lignin derived from waste pulping black liquor via crude extraction is directly converted into high-performance PC for a very short duration of 10–30 min by microwave heating. The inherent inorganic salts in crude lignin with a high content of 17.3% is innovatively used as initial microwave absorber to achieve rapid conversion from lignin into bio-char, and further as porogen combined with KOH to synergistically obtain well-developed porous texture. The resultant PC possesses a super high specific surface area of 3065 m 2 g −1 , hierarchical pore size distribution with abundant micropores (0.73 cm 3 g −1 ) and a remarkable meso-/macropores ratio of 64.4%, highly disordered and amorphous structure, as well as oxygen-enriched structure with a surface oxygen content up to 16.5%. These attractive characteristics contribute to excellent electrochemical properties of the resultant supercapacitor electrode which exhibits a high specific capacitance of 325 F g −1 at 0.5 A g −1 in 6 mol L −1 KOH electrolyte, still maintaining a high value of 258 F g −1 (79.4%) at 50 A g −1 . The prepared supercapacitor can remain 81.9% energy density when the power density was increased by 20 folds, suggesting its excellent energy-power synergetic outputting property. These attractive results pave a new way to utilize such a biomass waste, especially with high inorganic salts content, into value-added electrode material for advanced energy storage application. • Conversion from waste lignin into porous carbon only required 10–30 min. • Inorganic salts act as microwave absorber and also porogen. • Super high specific surface areas surpassing 3000 m 2 g −1 were achieved. • A remarkably high rate capability of 79.4% was achieved at 50 A g −1 .

Microwave Assisted KOH Activation of Salacca Peel Dericed Activated Carbons as Adsorbents for Methylene Blue Removal from Aqueous Phase

In this study, salacca peel derived activated carbons (SPAC) were prepared by microwave assisted- KOH activation process. In the preparation process, the fixed mass ratio between salacca peel and KOH of 1:2 was used. Next, the effects of activation time (5, 15, 20 and 25 minutes) and microwave power (30, 380 and 700 W) on the characteristics of SPAC were then investigated. The BET surface area of SPAC was about 1491 m2/g for activation time of 25 minutes and microwave power of 700 W. The as-prepared SPAC was then then as adsorbents for methylene blue (MB) removal from aqueous phase. The adsorption data of SPAC were analyzed by Langmuir and Freundlich adsorption isotherms and the best correlation was shown by the Langmuir isotherm with maximum capacity of 327.9 mg/g. The analyses of kinetic data showed that the adsorption of MB on SPAC follow the pseudo-second order kinetic model.

Competitive adsorption of naphthalene and phenanthrene on walnut shell based activated carbon and the verification via theoretical calculation.

Walnut shell based activated carbon (WAC) was prepared via microwave-assisted KOH activation. The adsorption behaviors towards naphthalene (NAP) and phenanthrene (PHE) over WAC were studied, both in single- and binary-compound systems. Characterization results reveal the excellent microporous structure of WAC, with a micropore specific surface area of 438.5 m2 g−1. The functional groups of walnut shell precursor surface were activated through microwave irradiation. In both systems, the pseudo-second-order model can better describe the adsorption kinetic data of PAHs over WAC at all experimental conditions. Mass transfer mechanism analysis shows that film diffusion was the rate-limiting step during the adsorption process. The adsorption amount of PAHs on WAC decreased as pH values increased, and the equilibrium data can be fitted by the Freundlich isotherm model well. In binary-component systems, the presence of PHE prominently restrained the adsorption towards NAP, and the Sheindorf–Rebhun–Sheintuch (SRS) model can fully fit the adsorption equilibrium experimental values of PAHs over WAC. In addition, the preferential adsorption behavior of PHE over WAC also was confirmed by theoretical calculations. The π–π complex between the active sites on the WAC surface and π-electrons of benzene rings from PAHs may play a major role in competitive adsorption. These results indicated that WAC was a potentially low-cost adsorbent for PAH elimination.

Waste phenolic resin derived activated carbon by microwave-assisted KOH activation and application to dye wastewater treatment

Abstract The waste phenolic resin was utilized as the raw material to prepare activated carbon (AC) used KOH as the activating agent via microwave heating. The phenolic resin was carbonized at 500°C and then performed with a KOH/Char ratio of 4 and microwave power of 700 W for a duration of 15 min. The physic-chemical characteristics of the AC were characterized by N2 adsorption instrument, FTIR, SEM and TEM. The BET surface area and pore volume of AC were found to be 4269 m2/g and 2.396 ml/g, respectively. The activation process to generate such a phenomenally high surface area of the AC has little reported in open literatures and could pave way for preparation adsorbents that are far superior to the currently marketed adsorbents. The methylene blue (MB) was used as the model to assess its suitability to dye wastewater treatment. Towards this, the MB adsorption isotherms were conducted at three different temperatures and tested with different adsorption isotherm models. The adsorption isotherms could be modeled using Langmuir isotherm. While the kinetics could be used the pseudo-second order kinetics to describe. Thermodynamic results demonstrated that the adsorption process was a spontaneous, as well as an endothermic.

Preparation of High Surface Area Activated Carbon from Spent Phenolic Resin by Microwave Heating and KOH Activation

AbstractThe spent phenolic resin is as raw material for preparing high surface area activated carbon (HSAAC) by microwave-assisted KOH activation. The effects of microwave power, activation duration and impregnation ratio (IR) on the iodine adsorption capability and yield of HSAAC were investigated. The surface characteristics of HSAAC were characterized by nitrogen adsorption isotherms, FTIR, SEM and TEM. The operating variables were optimized utilizing the response surface methodology (RSM) and were identified to be microwave power of 700 W, activation duration of 15 min and IR of 4, corresponding to a yield of 51.25 % and an iodine number of 2,384 mg/g. The pore structure parameters of the HSAAC, i. e., Brunauer–Emmett–Teller (BET) surface area, total pore volume, and average pore diameter were estimated to be 4,269 m2/g, 2.396 ml/g and 2.25 nm, respectively, under optimum conditions. The findings strongly support the feasibility of microwave-assisted KOH activation for preparation of HSAAC from spent phenolic resin.

Large surface area activated carbon from low-rank coal via microwave-assisted KOH activation for methylene blue adsorption

Large surface area activated carbon from low-rank coal via microwave-assisted KOH activation for methylene blue adsorption

Preparation Activated Carbon from Scrap Tires by Microwave Assisted KOH Activation for Removal Emulsified Oil

In this paper activated carbon adsorbents produced from waste tires by chemical activation methods and application of microwave assisted KOH activation. The influence of radiation time, radiation power, and impregnation ratio on the yield and oil removal which is one of the major environmental issues nowadays and considered persistent environmental contaminants and many of them are suspected of being carcinogenic. Based on Box-Wilson central composite design, polynomial models were developed to correlate the process variables to the two responses. From the analysis of variance the significant variables on each response were identified. Optimum conditions of 4 min radiation time, 700 W radiation power and 0.5 g/g impregnation ratio gave 205.8749 mg/g oil removal and 35.19618 % yield. The characteristics of the AC were examined by pore structure analysis, and scanning electron microscopy (SEM).The BET surface area and total pore volume were identified to be 374.594 m²/g and 0.2039 m³/g, respectively.

3D interconnected porous carbons from MOF-5 for supercapacitors

3D interconnected porous carbons (IPCs) as supercapacitor electrode materials were prepared from MOF-5 via microwave-assisted KOH activation. The results show that the BET surface area of as-made IPCs is tunable from 798 to 1595m2g−1. IPC3-M made at 3 of MOF-5/KOH mass ratio shows a high capacitance up to 212Fg−1 in 6m KOH aqueous electrolyte at a current density of 0.05Ag−1. IPC electrodes also exhibit excellent rate capability (82.9% capacitance retention as the current density increases from 0.05 to 20Ag−1) and superior cycle stability (95.9% capacitance retention after 1000 cycles) due to short distance for ion fast transport, abundant accessible pores for ion storage and interconnected architecture for electron conduction.

Amoxicillin adsorption on microwave prepared activated carbon from Arundo donax Linn: Isotherms, kinetics, and thermodynamics studies

Microwave-assisted KOH activation of renewable biomass Arundo donax Linn was adopted for preparation of activated carbon (KAC) with high capacity for amoxicillin antibiotic (AMX). The characteristics of KAC were examined by proximate and pore structure analyses, scanning electron microscopy (SEM) and Fourier transforms infrared spectroscopy (FTIR). The ash and moisture contents of KAC were 5.5 and 0.5% compared to 2.2 and 2.1% for raw biomass. The BET surface area and total pore volume were identified to be 1065.3m3/g and 0.643cm2/g, respectively. The best preparation conditions in terms of KAC yield and AMX uptake were reported as 10min radiation time, 620W radiation power and 2g/g impregnation ratio resulted in 9.1% yield and 196.9mg/g AMX uptake. Experimental equilibrium data for AMX adsorption were analyzed by Langmuir, Freundlich, and Sips isotherms. The results showed that the best fitting was achieved by Sips isotherm with high adsorption capacity of 345.4mg/g on KAC compared to 75.8mg/g on precursor. Also, kinetic data were correlated by pseudo-first order, pseudo-second order, and intra-particle diffusion models with well-fitting to pseudo-second order model. Thermodynamic analysis showed that adsorption enthalpy of AMX was 17.7kJ/mol which revealed endothermic and physisorptive nature under examined conditions.

Efficient preparation of porous carbons from coal tar pitch for high performance supercapacitors

Porous carbons (PCs) for supercapacitors were prepared from coal tar pitch by a one-step microwave-assisted KOH activation with low KOH consumption. The surface area of the PC (PC2–M) made at a KOH/pitch mass ratio of 2 with microwave heating for 30 min reaches 1786 m2/g. The electrochemical performance of the PC electrode for supercapacitors was evaluated in different electrolytes including KOH, K2SO4, Na2SO4, Li2SO4 in water, and tetraethylammoniatetra fluoroborate in propylene carbonate. The supercapacitors have a high specific capacitance of 267 F/g in 6 mol/L KOH aqueous electrolyte at 0.1 A/g and a high energy density of 12.0 Wh/kg at 1318 W/kg in a 0.5 mol/L K2SO4 neutral electrolyte. The one-step microwave-assisted KOH activation is a simple, efficient and low energy-consumption approach for the preparation of high performance PCs for supercapacitors.

Optimization of microwave preparation conditions for activated carbon from Albizia lebbeck seed pods for methylene blue dye adsorption

Microwave assisted KOH activation has been utilized for preparation of activated carbon from agricultural wastes, Albizia lebbeck seed pods. The surface area, micropores volume, and mesopores volume of this carbon (KAC) were 1824.88m2/g, 0.645cm3/g, and 0.137cm3/g, respectively. The effects of process variables represented by radiation time, radiation power, and impregnation ratio on the yield and methylene blue (MB) uptake of such carbon were studied. Box-Wilson central composite design was adopted to arrange the experiments and two second order polynomial models were developed to correlate the process variables to the two responses. MB uptake of 220.83mg/g and 22.48% carbon yield were reported at optimum preparation conditions. The best fitting for MB experimental equilibrium data was achieved with the Langmuir isotherm, giving a maximum MB adsorption capacity of 381.22mg/g. The experimental kinetic data were well described by the pseudo-second order model.

Preparation of nanoporous carbon microspheres by subcritical water carbonization and electrocapacitive study

In this work, sugar-derived carbon microspheres (CMSs) with diameters in the range of 5–10μm and uniform nanopores were prepared using the subcritical water carbonization method, followed by microwave-assisted KOH activation. The carbonization was conducted at 3MPa and moderate temperatures (150–170°C) in subcritical water, which is a green dehydrating agent. The formation of the CMSs from a sugar solution under subcritical water conditions followed a radical-catalysed emulsion polymerization mechanism. The specific surface area and pore volume of the CMSs were found to increase with increasing the mass ratio of KOH over carbon up to 1:1. Electrocapacitive results showed that a sample prepared at a KOH to carbon ratio of 1:1 and microwave irradiation level of 70% possessed the highest specific capacitance (about 179.2F/g) at a current density of 1A/g and excellent cycling performance over 1000 charging/discharging cycles without significantly loss in capacitance. The specific capacitance and capacitive retention of this electrode are comparable to that of an electrode prepared from commercial YP-80F activated carbon.

Fluoroquinolones antibiotics adsorption onto microporous activated carbon from lignocellulosic biomass by microwave pyrolysis

Microwave-assisted KOH activation has been adopted to prepare activated carbon from a lignocellulosic biomass, Albizia lebbeck seed pods. Fluoroquinolones antibiotics such as ciprofloxacin (CIP) and norfloxacin (NOR) were removed from aqueous solutions by adsorption on prepared carbon. The surface area, micropores volume, and mesopores volume of such carbon were 1824.88m2/g, 0.645cm3/g and 0.137cm3/g, respectively. The effects of pH, adsorbent dose, and contact time on the adsorptive removal process were studied. Maximum removal percentages of 96.12% and 98.13% were achieved for CIP and NOR adsorption, respectively. The best fitting for equilibrium adsorption data of both antibiotics was obtained by the Langmuir isotherm with maximum capacities of 131.14 and 166.99mg/g for CIP and NOR, respectively. The kinetic data were found to follow closely the pseudo-second order model for both antibiotics. Results of thermodynamic studies showed an endothermic CIP adsorption compared to an exothermic NOR adsorption under examined conditions.

Utilization of oil palm biodiesel solid residue as renewable sources for preparation of granular activated carbon by microwave induced KOH activation

In this work, preparation of granular activated carbon from oil palm biodiesel solid residue, oil palm shell (PSAC) by microwave assisted KOH activation has been attempted. The physical and chemical properties of PSAC were characterized using scanning electron microscopy, volumetric adsorption analyzer and elemental analysis. The adsorption behavior was examined by performing batch adsorption experiments using methylene blue as dye model compound. Equilibrium data were simulated using the Langmuir, Freundlich and Temkin isotherm models. Kinetic modeling was fitted to the pseudo-first-order, pseudo-second-order and Elovich kinetic models, while the adsorption mechanism was determined using the intraparticle diffusion and Boyd equations. The result was satisfactory fitted to the Langmuir isotherm model with a monolayer adsorption capacity of 343.94mg/g at 30°C. The findings support the potential of oil palm shell for preparation of high surface area activated carbon by microwave assisted KOH activation.

Microporous activated carbon from Siris seed pods by microwave-induced KOH activation for metronidazole adsorption

In this study, microwave-assisted KOH activation was adopted for preparation of a microporous activated carbon from an agricultural waste, Siris seed pods. Carbon with high BET surface area of 1824.88m2/g and 0.782cm3/g total pore volume has been obtained from these precursors. The influences of radiation time, radiation power, and impregnation ratio on yield and iodine number of prepared carbon have been studied and the best conditions were determined. The sorption mechanisms of a nitroimidazole antibiotic, metronidazole (MNZ), onto such carbon have been investigated. The adsorption data of MNZ were analyzed by Langmuir, Freundlich, and Temkin isotherms and the best correlation was achieved by the Langmuir isotherm with maximum capacity of 196.31mg/g. The analyses of kinetic data showed that the adsorption of MNZ on prepared carbon follow closely the pseudo-second order model. Results of thermodynamic studies showed endothermic and spontaneous natures of MNZ adsorption under examined conditions.

Synthesis of mesoporous carbons for supercapacitors from coal tar pitch by coupling microwave-assisted KOH activation with a MgO template

Mesoporous carbons (MCs) for supercapacitors were prepared from coal tar pitch by a microwave-assisted one-step process coupling the potassium hydroxide (KOH) activation and magnesium oxide (MgO) template. MCs were characterized by scanning electron microscope and X-ray diffraction. The results show that the specific surface area (SBET), micropore volume and specific capacitance of MCs made by microwave heating as well as the energy density of MC capacitors pass through a maximum with increasing mass of MgO and the relative mass ratio of KOH/pitch. The SBET of MCs varies from 1003 to 1394m2/g. The SBET and total pore volume of MC and microporous carbon made by microwave heating are bigger than that made by conventional heating. Under optimum conditions with the masses of coal tar pitch, MgO, KOH at 9g, 12g, 6g, and the microwave power at 600W, MC (MC9-12-6) made at 30min heating time shows a high specific capacitance of 224F/g in 6M KOH aqueous electrolyte after 1000 cycles. The results have shown that microwave-assisted rapid KOH activation coupled with the MgO template is an efficient one-step approach to the preparation of low cost yet high performance MCs for supercapacitors.

Adsorption characteristics of industrial solid waste derived activated carbon prepared by microwave heating for methylene blue

The main objective of this work is to prepare and characterize activated carbon form oil palm fiber (PFAC), an industrial solid waste abundantly available from the biodiesel manufacturing plants, via microwave assisted KOH activation. The influences of chemical impregnation ratio (0.25–2.00), microwave power (90–800W) and radiation time (2–8min) on the properties of activated carbon were investigated. The adsorptive behavior of PFAC was quantified using methylene blue (MB) as dye model compound, while the surface chemistry was characterized by determination of surface acidity/basicity, Fourier transform infrared spectroscopy and zeta potential measurement. Equilibrium data were examined using a comparison of linear and non-linear isotherm models. The optimum conditions resulted in PFAC with a monolayer adsorption capacity of 382.32mg/g for MB and carbon yield of 32.09%. The BET surface area, Langmuir surface area and total pore volume were determined to be 1223m2/g, 1827m2/g and 0.72cm3/g, respectively. The adsorption kinetic was well fitted to the pseudo-second-order model.