Synthesis of graphene oxide nano-materials coated bio-char using carbonaceous industrial waste for phenol separation from water

Activated carbon prepared from Brazil nut shells towards phenol removal from aqueous solutions

The Brazil nut shell was used as a precursor material for preparing activated carbon by chemical activation with potassium hydroxide. The obtained material (BNSAC) was characterized, and the adsorptive features of phenol were investigated. The characterization showed that the activated carbon presented several rounded cavities along the surface, with a specific surface area of 332 m2 g-1. Concerning phenol adsorption, it was favored using an adsorbent dosage of 0.75 g L-1 and pH 6. The kinetic investigation revealed that the system approached the equilibrium in around 180 min, and the Elovich model represented the kinetic curves. The Sips model well represented the equilibrium isotherms. In addition, the increase in temperature from 25 to 55 °C favored the phenol adsorption, increasing the maximum adsorption capacity value (qs) from 83 to 99 mg g-1. According to the estimated thermodynamic parameters, the adsorption was spontaneous, favorable, endothermic, and governed by physical interactions. Therefore, the Brazil nut shell proved a good precursor material for preparing efficient activated carbon for phenol removal.

Novel Concepts for Graphene-Based Nanomaterials Synthesis for Phenol Removal from Palm Oil Mill Effluent (POME)

In recent years, the global population has increased significantly, resulting in elevated levels of pollution in waterways. Organic pollutants are a major source of water pollution in various parts of the world, with phenolic compounds being the most common hazardous pollutant. These compounds are released from industrial effluents, such as palm oil milling effluent (POME), and cause several environmental issues. Adsorption is known to be an efficient method for mitigating water contaminants, with the ability to eliminate phenolic contaminants even at low concentrations. Carbon-based materials have been reported to be effective composite adsorbents for phenol removal due to their excellent surface features and impressive sorption capability. However, the development of novel sorbents with higher specific sorption capabilities and faster contaminant removal rates is necessary. Graphene possesses exceptionally attractive chemical, thermal, mechanical, and optical properties, including higher chemical stability, thermal conductivity, current density, optical transmittance, and surface area. The unique features of graphene and its derivatives have gained significant attention in the application of sorbents for water decontamination. Recently, the emergence of graphene-based adsorbents with large surface areas and active surfaces has been proposed as a potential alternative to conventional sorbents. The aim of this article is to discuss novel synthesis approaches for producing graphene-based nanomaterials for the adsorptive uptake of organic pollutants from water, with a special focus on phenols associated with POME. Furthermore, this article explores adsorptive properties, experimental parameters for nanomaterial synthesis, isotherms and kinetic models, mechanisms of nanomaterial formation, and the ability of graphene-based materials as adsorbents of specific contaminants.

Facile fabrication of robust, versatile, and recyclable biochar-graphene oxide composite monoliths for efficient removal of different contaminants in water

Water pollution produced by various contaminants is presently a major worldwide issue, posing a significant challenge to the development of novel materials for water treatment. Herein, robust and recyclable biochar-graphene oxide (BC-GO) composite monoliths were prepared utilizing lignin precursor as a carbon source in a one-pot hydrothermal process free of hazardous chemicals. Characterization results indicated the BC-GO composite monolith had abundant microchannels, nanopores, and a large specific surface area, thereby exhibiting a high adsorption capacity of 796.8 mg g^-1 to doxycycline in water, which was superior to conventional adsorbents. Furthermore, by annealing the BC-GO composite monolith, it could be transformed to hydrophobic (CA = 140°). The annealed BC-GO composite monolith retained a pronounced porous structure with a larger surface area and showed exceptional absorption capabilities of 55-130 g g^-1 toward various oils and solvents, which were higher/comparable to previously reported graphene-based materials. In addition, both BC-GO composite monoliths were highly stable and could be reused for a number of cycles of pollutants removal. The simplicity, environmental friendliness, and effectiveness of our approach to building BC-GO composite monoliths may pave the way for their future applications in the field of water purification.

Utilization of rice husk wastes in synthesis of graphene oxide-based carbonaceous nanocomposites

Rice husk is an agricultural waste-based biomass that can provide an alternative renewable source of bioenergy. Rice husk carbon and rice husk ash are major solid residues obtained after converting rice husk to bioenergy. This paper reports the synthesis of two graphene oxide-based activated carbons using rice husk carbon through H₃PO₄ and ZnCl₂ activation, respectively. By contrast, mesoporous silica was produced using recycled rice husk ash. Graphene oxide/ordered mesoporous carbon was prepared using mesoporous silica as a template source. These composites were inspected using a Raman spectrometer, Fourier transform infrared spectrometer, transmission electron microscope, field-emission scanning electron microscope, X-ray diffractometer, and surface area analyzer. Experimental results indicated that graphene oxide-based H₃PO₄ activated carbon, ZnCl₂ activated carbon, and ordered mesoporous carbon had a surface area of 361, 732, and 936 m²/g, respectively; a pore volume of 0.299, 0.581, and 1.077 cm³/g, respectively; and an average pore size of 2.31, 3.17, and 4.35 nm, respectively. The carbonaceous composites with graphene oxide exhibited a higher adsorption ability than did pure carbon materials without graphene oxide. The maximum adsorption capacities using methylene blue as adsorbate followed the order of ordered mesoporous carbon (1591 mg/g) > ZnCl₂ activated carbon (899 mg/g) > H₃PO₄ activated carbon (747 mg/g). The isothermal adsorption and kinetics study for graphene oxide/ordered mesoporous carbon indicated that adsorption followed the Langmuir isotherm model and pseudo-second order kinetic model. Rice husk waste has excellent prospective potential for producing highly valuable nanoproducts and for reducing environmental pollution.

Phenol adsorption on high microporous activated carbons prepared from oily sludge: equilibrium, kinetic and thermodynamic studies

The purpose of this study was the preparation, characterization and application of high-performance activated carbons (ACs) derived from oily sludge through chemical activation by KOH. The produced ACs were characterized using iodine number, N₂ adsorption-desorption, Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The activated carbon prepared under optimum conditions showed a predominantly microporous structure with a BET surface area of 2263 m² g⁻¹, a total pore volume of 1.37 cm³ g⁻¹ and a micro pore volume of 1.004 cm³ g⁻¹. The kinetics and equilibrium adsorption data of phenol fitted well to the pseudo second order model (R² = 0.99) and Freundlich isotherm (R² = 0.99), respectively. The maximum adsorption capacity based on the Langmuir model (434 mg g⁻¹) with a relatively fast adsorption rate (equilibrium time of 30 min) was achieved under an optimum pH value of 6.0. Thermodynamic parameters were negative and showed that adsorption of phenol onto the activated carbon was feasible, spontaneous and exothermic. Desorption of phenol from the adsorbent using 0.1 M NaOH was about 87.8% in the first adsorption/desorption cycle and did not decrease significantly after three cycles. Overall, the synthesized activated carbon from oily sludge could be a promising adsorbent for the removal of phenol from polluted water.