Characterization and phenol adsorption performance of activated carbon prepared from tea residue by NaOH activation

Impacts of controlled microwave field irradiation on o-cresol and p-cresol adsorption capability of activated carbon

To access the feasibility of microwave in promoting adsorbability of carbonaceous adsorbents, microwave irradiation on activated carbon (AC) was conducted at powers of 400-800 W and duration of 10 min. Accordingly, the temperature rising of AC under microwave field were studied. Moreover, the alterations in physicochemical properties of AC and impacts on cresol isomer adsorption were investigated. Results indicated that the heating curve of AC displays the initial fast temperature rising stage and the final slow stage. Additionally, the bulk temperature at irradiation terminal increases with microwave power. The temperature rising further increases the pores with a diameter range of 1.00-6.00 nm of AC; it also increases the oxygenic functional groups of AC after irradiation at 400 W and 800 W, but decreases that of AC after irradiation at 640 W. The saturation adsorption capacity of o-cresol and p-cresol on the irradiated AC rises with elevated temperature. Additionally, the cresol isomer adsorption kinetics on the irradiated AC follows the Elovich model. The above-mentioned equilibrium and kinetics suggest that the cresol isomer adsorption on the irradiated AC is dominant by chemisorption. Finally, the optimum irradiation power for o-cresol and p-cresol adsorption is 800 W and 400 W, respectively, thereby fabricating AC with developed pores and abundant oxygenic functional groups. Accordingly, the saturation adsorption capacity of o-cresol and p-cresol reaches up to 111.11 mg·g-1 and 95.97 mg·g-1, respectively. Overall, microwave irradiation is a viable option to promote cresol isomer adsorption on AC.

Enhanced adsorption of phenolic compounds using biomass-derived high surface area activated carbon: Isotherms, kinetics and thermodynamics

The progress of industrial and agricultural pursuits, along with the release of inadequately treated effluents especially phenolic pollutant, has amplified the pollution load on environment. These organic compounds pose considerable challenges in both drinking water and wastewater systems, given their toxicity, demanding high oxygen and limited biodegradability. Thus, developing an eco-friendly, low-cost and highly efficient adsorbent to treat the organic pollutants has become an important task. The present investigation highlights development of a novel adsorbent (CFPAC) by activation of Cassia fistula pod shell for the purpose of removing phenol and 2,4-dichlorophnenol (2,4-DCP). The significant operational factors (dosage, pH, concentration, temperature, speed) were also investigated. The factors such as pH = 2 and T = 20°C were found to be significant at 1.6 g/L and 0.6 g/L dosage for phenol and 2,4-DCP respectively. Batch experiments were further conducted to study isotherms, kinetic and thermodynamics studies for the removal of phenol and 2,4-DCP. The activated carbon was characterised as mesoporous (specific surface area 1146 m2/g, pore volume = 0.8628 cc/g), amorphous and pHPZC = 6.4. At optimum conditions, the maximum sorption capacity for phenol and 2,4-DCP were 183.79 mg/g and 374.4 mg/g respectively. The adsorption isotherm was better conformed to Redlich Peterson isotherm (phenol) and Langmuir isotherm (2,4-DCP). The kinetic study obeyed pseudo-second-order type behaviour for both the pollutants with R2 > 0.999. The thermodynamic studies and the value of isosteric heat of adsorption for both the pollutants suggested that the adsorption reaction was dominated by physical adsorption (ΔHx < 80 kJ/mol). Further, the whole process was feasible, exothermic and spontaneous in nature. The overall studies suggested that the activated carbon synthesised from Cassia fistula pods can be a promising adsorbent for phenolic compounds.

Optimization of preparation conditions of a novel low-cost natural bio-sorbent from olive pomace and column adsorption processes on the removal of phenolic compounds from olive oil mill wastewater

Olive oil mill wastewater (OMWW) poses an undeniable environmental problem due to its high organic loads and phenolic compound (PC) content. This study determined the optimal conditions for preparing a new bio-sorbent from olive pomace (OP) and the adsorptive treatment of OMWW by this bio-sorbent. The activation reaction was performed with hydrogen peroxide. The results of the combination effect optimization of the three preparation variables, the activation temperature (°C) X₁, the activation time (min) X₂, and the impregnation ratio X₃, are presented by the response surface methodology (RSM). The maximum adsorption capacity was obtained at an activation time of 240 min, a temperature of 80 °C, and a ratio equal to 6.2:1. The bio-sorbent was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometer (XRD). The adsorption process performance of this bio-sorbent was examined in batch (phenol solution) and fixed-bed columns (real effluent of OMWW). An adsorption capacity of 789.28 mg g^-1 and 643.92 mg g^-1 has been achieved for 4000 mg L^-1 concentration of PCs, respectively, for batch and fixed-bed column essays. The adsorption isotherm and kinetics were consistent with the Langmuir and pseudo-second-order models. Therefore, the Thomas model best fits the fixed-bed column experimental data. The bio-sorbent gave a high desorption percentage of PCs, which was above 60% using HCl (0.1M).

Recent Advanced Supercapacitor: A Review of Storage Mechanisms, Electrode Materials, Modification, and Perspectives

In recent years, the development of energy storage devices has received much attention due to the increasing demand for renewable energy. Supercapacitors (SCs) have attracted considerable attention among various energy storage devices due to their high specific capacity, high power density, long cycle life, economic efficiency, environmental friendliness, high safety, and fast charge/discharge rates. SCs are devices that can store large amounts of electrical energy and release it quickly, making them ideal for use in a wide range of applications. They are often used in conjunction with batteries to provide a power boost when needed and can also be used as a standalone power source. They can be used in various potential applications, such as portable equipment, smart electronic systems, electric vehicles, and grid energy storage systems. There are a variety of materials that have been studied for use as SC electrodes, each with its advantages and limitations. The electrode material must have a high surface area to volume ratio to enable high energy storage densities. Additionally, the electrode material must be highly conductive to enable efficient charge transfer. Over the past several years, several novel materials have been developed which can be used to improve the capacitance of the SCs. This article reviews three types of SCs: electrochemical double-layer capacitors (EDLCs), pseudocapacitors, and hybrid supercapacitors, their respective development, energy storage mechanisms, and the latest research progress in material preparation and modification. In addition, it proposes potentially feasible solutions to the problems encountered during the development of supercapacitors and looks forward to the future development direction of SCs.

Performance and dynamic modeling of a continuously operated pomace olive packed bed for olive mill wastewater treatment and phenol recovery

The solid waste of olive oil extraction processes (olive pomace, OP) was converted into activated carbon (AC) by treating it with NaOH and then encapsulating it within sodium alginate (SA) in beads by crosslinking (SA-AC beads). The prepared SA-AC beads were utilized as an adsorbent for the elimination and recovery of phenolic compounds (PCs) from olive mill wastewater (OMWW) following a zero liquid and waste discharge approach to implement and promote the circular economy concept. The novel AC and SA-AC beads were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and Brunauer, Emmett and Teller (BET) analysis. The adsorption performance of these beads was evaluated in batch and fixed-bed reactors operated in a concurrent flow system. The results revealed that an adsorption capacity of 68 mg g^-1 was attained for 4000 mg L^-1 phenolic compounds. The kinetics of the adsorption process of the PCs fit a pseudo second-order model, and the most likely mechanism took place in two stages. The adsorption isotherm conformed to the Langmuir model, representing the monolayer adsorption of the phenolic compounds. The dynamic models were used, and they accurately represented the breakthrough curves. Considering PC recovery and process reusability, a regeneration experiment of SA-AC beads was carried out in fixed-bed reactors. SA-AC beads showed a high percentage desorption >40% using ethanol and were efficient after several cycles of OMWW treatment and phenol recovery.

A Promising Solution for Food Waste: Preparing Activated Carbons for Phenol Removal from Water Streams

Phenol and its derivatives are highly toxic chemicals and are widely used in various industrial applications. Therefore, the industrial wastewater streams must be treated to lower the concentration of phenol before discharge. At the same time, food waste has been a major environmental problem globally and the scientific community is eagerly seeking effective management solutions. The objective of this study was to understand the potential of utilizing food waste as a renewable and sustainable resource for the production of activated carbons for the removal of phenol from water streams. The food waste was pyrolyzed and physically activated by steam. The pyrolysis and activation conditions were optimized to obtain activated carbons with high surface area. The activated carbon with the highest surface area, 745 m2 g-1, was derived via activation at 950 °C for 1 h. A detailed characterization of the physicochemical and morphological properties of the activated carbons derived from food waste was performed and a comprehensive adsorption study was conducted to investigate the potential of using the activated carbons for phenol removal from water streams. The effects of pH, contact time, and initial concentration of phenol in water were studied and adsorption models were applied to experimental data to interpret the adsorption process. A remarkable phenol adsorption capacity of 568 mg g-1 was achieved. The results indicated that the pseudo-second-order kinetic model was better over the pseudo-second-order kinetic model to describe the kinetics of adsorption. The intraparticle diffusion model showed multiple regions, suggesting that the intraparticle diffusion was not the sole rate-controlling step of adsorption. The Langmuir isotherm model was the best model out of Freundlich, Temkin, and Dubinin-Radushkevich models to describe the phenol adsorption on activated carbons derived from food waste. This study demonstrated that food waste could be utilized to produce activated carbon and it showed promising capacity on phenol removal.

Laccase production by Trametes versicolor in solid-state fermentation using tea residues as substrate and its application in dye decolorization

An efficient valorization of tea residues into value-added product was developed by Trametes versicolor in solid-state fermentation (SSF). The laccase production of 25.7 U/g dry substrate was obtained by optimizing culture medium and condition, resulting in a 4.0-fold increase compared to that of 6.4 U/g dry substrate under unoptimized condition. During the 7-day cultivation under SSF, 44.7%, 12.2% and 9.8% degradation occurred for lignin, hemicellulose and cellulose in tea residues, respectively. Laccase production reached 31.2 U/g dry substrate by the scaling-up culture in shallow tray system. The dry fermented tea residues were directly used as crude enzyme in the decolorization of malachite green. It possessed a decolorization rate of more than 95% within 120 min and remained 81.3% of decolorization capacity after 6 cycles. The present study provided a useful strategy for low-cost laccase production by SSF and it exhibited great potential for the application in dye decolorization.

Pore morphology and fractal dimension of ash deposited in catalyst diesel particulate filter

Diesel particle filter (DPF) has been widely acknowledged as the most effective way to mitigate particulate matter emitted from diesel engines. Over time, ash mainly derived from lubricating oil will deposit in DPF, showing negative influence to engine performance, fuel economy, service life of DPF, and so on. Recently, the investigation about DPF backpressure characteristics and DPF regeneration process considering ash has gained attention. As a porous material, ash will play a key role in the DPF permeability. Thus, the pore morphology and fractal dimension of ash derived from three kinds of lube are addressed in this work. The results show that the changing tendency of the micropore specific surface and pore volume is consistent with the ash content in lubricant oil, which is owing to the chemical interaction of Ca and S contained in the oil during the complex DPF regeneration. There is no significant changing tendency of the mesopore and macropore properties because of the heterogeneity and complexity of ash. According to the fractal analyses, the Avnir equation shows excellent predictive accuracy for the pore surface fractal dimension of ash, which reflects that the ash pore surfaces are irregular.

The performance of sulphur doped activated carbon supercapacitors prepared from waste tea

The pore structure, high surface area and good conductivity are the key properties for the electrochemical double layer based supercapacitors. The activated carbons were produced from the waste tea, utilising microwave pretreatment with H₃PO₄ and activation at 450°C. Sodium thiosulfate pentahydrate (Na₂S₂O₃·5H₂O) was used as sulphur doping agent at 800°C to enhance conductivity of the activated carbons. Supercapacitor electrodes were prepared from both the activated carbon (WTAC) and sulphur doped activated carbon (WTAC-S) samples and the electrochemical performances were tested in the presence of 6 M KOH and 1 M H₂SO₄ as electrolytes. The activated carbon samples were characterised by Brunauer-Emmett-Teller (BET) surface area, Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM/EDS) and Fourier Transform Infrared Spectroscopy (FTIR) analysis techniques. The electrochemical performance analyses were performed by galvanostatic charge-discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. The specific capacitance values of the WTAC and WTAC-S samples under the 1 A g^-1 current density were found to be 89.3, 144.7 F g^-1 for KOH electrolyte and 73.8 and 101.9 F g^-1 for H₂SO₄ electrolyte, respectively. The results show that the sulphur doping process enhances the electrochemical performance of activated carbon samples.

Aerobic denitrification performance and nitrate removal pathway analysis of a novel fungus Fusarium solani RADF-77

Increasing nitrogenous contaminants have caused immense challenges to the environment and human health. As compared to physical and chemical methods, biological denitrification is considered to be an effective solution due to its environmental friendliness, high efficiency, and low cost. In the present work, a novel fungal strain identified as Fusarium solani (RADF-77) was isolated from cellulose material-supported denitrification reactor; this strain is capable of removing nitrogen under aerobic conditions. The average NO₃^--N removal rate for RADF-77 were 4.43 mg/(L·h) and 4.50 mg/(L·d), when using glucose and tea residue as carbon source, respectively. The nitrogen balance revealed that 53.66% of N vanished via gaseous products. Transcriptional results revealed that respiratory and assimilative nitrate reductases may work together for nitrate removal. Our results indicate that RADF-77 could be used as a potential means of enhancing nitrate-removal performance, as well as recycling tea residue, which is the main byproduct of the manufacture of tea extracts.

Equilibrium, kinetic and thermodynamic studies of removal of phenol from aqueous solution using surface engineered chemistry

Iron impregnated activated carbon has been used as a new adsorbent for the adsorptive removal of phenol from waste water. Impregnation of iron was confirmed by Fourier transform infrared spectroscopy and scanning electron microscope and energy dispersive spectroscopy. Different parameters affecting the adsorption capacity of Iron impregnated activated carbon such as Iron impregnated activated carbon dosage, contact time, pH of solution, initial concentration of phenol and agitation speed were optimized. The residual concentration of phenol was determined by UV-Vis spectroscopy. Maximum adsorption efficiency was calculated 98.5% at optimized parameters: concentration of phenol 25 mg L⁻¹, Iron impregnated activated carbon dose 75 mg, pH 7.0 and agitation time 90 min. The experimental data was fitted to different adsorption isotherms and adsorption capacities obtained were 20 and 15 mg g⁻¹, respectively. Adsorption energy was found to be 1.54 kJ mol⁻¹ which predicts that phenol was adsorbed onto the Iron impregnated activated carbon through physisorption.