KOH Modification Research Articles

Development of a new adsorbent from pumpkin husk by KOH-modification to remove copper ions.

Heavy metal pollution in watercourses is a major environmental problem throughout the world due to rapid population growth, industrialization, and economic development. Considering this, the present study aimed to develop a new adsorbent from pumpkin husk (PH) by KOH modification to remove copper (Cu2+) ions and to explore its adsorptive potential. The sorption studies of Cu2+ on KOH-modified PH were carried out as functions of particle size, solution pH, adsorbent dose, temperature, initial metal concentration, and contact time. The sorption capacity of KOH-modified PH was found to be higher than that of raw PH, as 19.4 and 10.2mgg-1, respectively. Morphology and surface structures of adsorbents were characterized by determination of zero point charge, a Fourier transform infrared spectrometer (FTIR-ATR) spectra, and a scanning electron microscopy (SEM) of PH powders before and after the sorption of Cu2+. The pHzpc of PH was found to be 5.0. FTIR-ATR analyses indicated that amino, amide, hydroxyl, carboxyl, and oxygenated groups of PH play an important role in the sorption process. Sorption isotherm, kinetic, and thermodynamic parameters of Cu2+ on KOH-modified PH were studied. The kinetic process was well represented by the Logistic model. The maximum sorption was found as 73.16mgg-1 according to the well-fitting of Langmuir isotherm. Results of sorption and thermodynamic studies indicated that the process was exothermic, being feasible, and spontaneous. KOH-modified PH as an eco-friendly adsorbent had great potential to remove Cu2+ ions from aquatic system.

Eucalyptus sawdust derived biochar generated by combining the hydrothermal carbonization and low concentration KOH modification for hexavalent chromium removal

In this study, Eucalyptus sawdust was hydrothermally carbonized, and the resulting biochar was modified by a low concentration potassium hydroxide. The morphology and surface property was characterized by SEM-EDS, BET, FTIR and XPS techniques. A series of batch adsorption experiments were conducted to screen out the optimum conditions, and to investigate the isotherm, kinetics and thermodynamic behaviors. The results indicated that a high adsorption capacity of hexavalent chromium (qe 45.88 mg/g) was achieved by the combining of hydrothermal carbonization at 220 °C and 0.05 N potassium hydroxide modification, and a high biochar yield (47.61%) was obtained. The isotherm, kinetics and thermodynamic studies suggested that the spontaneously and endothermically chemical adsorption was the main mechanism, which was partially supported by BET, FTIR and XPS results. This finding suggested that the combination of hydrothermal carbonization and a subsequent low alkali modification was an effective method to prepare a high-performance adsorbent for hexavalent chromium removal.

Controlling coke deactivation and cracking selectivity of MFI zeolite by H3PO4 or KOH modification

The effect of the basic (KOH) or acid (H3PO4) treatment of the MFI (HZSM-5) zeolite has been studied comparing the structural and acidic features with the catalytic performance and deactivation of a set of unmodified and modified zeolites (SiO2/Al2O3=30–280, 0–3wt% of K or P). The properties of the catalysts have been elucidated using XRD, 27Al and 29Si NMR, N2 adsorption–desorption, and adsorption-TPD of tert-butylamine. The catalytic performance has been evaluated in the cracking of 1-butene by means of initial, 5h on-stream activity and coke formation. Our results point to the fact that using zeolites with high SiO2/Al2O3 ratio or neutralizing the strongest acid sites with KOH or H3PO4 increases propylene selectivity while decreases 1-butene conversion. The overall pathway of reaction involves propylene and other olefins as primary products that condensate in further steps to aromatics and ultimately to coke. This pathway can be controlled with less severe acidic features and by desilication with KOH or H3PO4 (particularly with the former).

Characterization of potassium hydroxide (KOH) modified hydrochars from different feedstocks for enhanced removal of heavy metals from water.

Hydrochars produced from different feedstocks (sawdust, wheat straw, and corn stalk) via hydrothermal carbonization (HTC) and KOH modification were used as alternative adsorbents for aqueous heavy metals remediation. The chemical and physical properties of the hydrochars and KOH-treated hydrochars were characterized, and the ability of hydrochars for removal of heavy metals from aqueous solutions as a function of reaction time, pH, and initial contaminant concentration was tested. The results showed that KOH modification of hydrochars might have increased the aromatic and oxygen-containing functional groups, such as carboxyl groups, resulting in about 2-3 times increase of cadmium sorption capacity (30.40-40.78 mg/g) compared to that of unmodified hydrochars (13.92-14.52 mg/g). The sorption ability among different feedstocks after modification was as the following: sawdust > wheat straw > corn stack. Cadmium sorption kinetics on modified hydrochars could be interpreted with a pseudo-second order, and sorption isotherm was simulated with Langmuir adsorption model. High cadmium uptake on modified hydrochars was observed over the pH range of 4.0-8.0, while for other heavy metals (Pb(2+), Cu(2+), and Zn(2+)) the range was 4.0-6.0. In a multi-metal system, the sorption capacity of heavy metals by modified hydrochars was also higher than that by unmodified ones and followed the order of Pb(II) > Cu(II) > Cd(II) > Zn(II). The results suggest that KOH-modified hydrochars can be used as a low cost, environmental-friendly, and effective adsorbent for heavy metal removal from aqueous solutions.

Effect of surface modification of carbon felts on capacitive deionization for desalination

Surface modified carbon felts were utilized as an electrode for the removal of inorganic ions from seawater. The surfaces of the carbon felts were chemically modified by alkaline and acidic solutions, respectively. The potassium hydroxide (KOH) modified carbon felt exhibited high Brunauer-Emmett-Teller (BET) surface areas and large pore volume, and oxygen-containing functional groups were increased during KOH chemical modification. However, the BET surface area significantly decreased by nitric acid (<TEX>$HNO_3$</TEX>) chemical modification due to severe chemical dissolution of the pore structure. The capability of electrosorption by an electrical double-layer and the efficiency of capacitive deionization (CDI) thus showed the greatest enhancement by chemical KOH modification due to the appropriate increase of carboxyl and hydroxyl functional groups and the enlargement of the specific surface area.

Reduction of [Fe(III)EDTA]− catalyzed by activated carbon modified with KOH solution

NO and SO2 can be eliminated simultaneously by [Fe(II)EDTA]2− solution with a pH range of 5.6–8.0 at 25–80°C. Activated carbon is used to catalyze the regeneration of [Fe(II)EDTA]2−. In this paper, KOH solution has been utilized to modify the carbon to improve its catalytic capability. Experimental results show that the optimal modification factors are as follow: KOH concentration 6.0moll−1, impregnation time 9h, activation temperature 700°C and activation time 4h. After KOH modification, the surface area of activated carbon decreases. But its basicity is enhanced, which plays an important role in improving the catalytic characteristics of activated carbon in the reduction of [Fe(III)EDTA]−. The experimental results demonstrate that the activated carbon modified by concentrated KOH solution can get a higher NO removal efficiency than the original activated carbon.

Influence of KOH modification on TiO 2 structure and Au/TiO 2 catalyst activity in CO oxidation

KOH-modified TiO 2 support was obtained by treating the hydrolysate of tetrabutyl titanate with KOH solution of various concentrations; the gold catalyst supported on the KOH-modified TiO 2 was prepared through impregnation and used for CO oxidation. The support and catalyst were characterized by N 2 physical sorption, thermogravimetry, thermo-analysis, X-ray powder diffraction, UV-vis diffuse reflection spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results indicate that the modification with KOH may influence the structure and property of TiO 2 and Au/TiO 2 significantly. KOH modification can change electronic structure of TiO 2 and enhance the activity of Au/TiO 2 catalyst for low-temperature CO oxidation. However, the modification with excessive KOH may also block the porous structure of TiO 2 and weaken its adsorption ability, which leads an enlargement of gold particles on Au/TiO 2 and a decrease of its catalytic activity for CO oxidation.

Nickel adsorption onto carbon anode dust modified by acetic acid and KOH

Carbon anode dust (CAD) is metallurgical waste material of aluminium production industry. The objective of this study was to convert carbon anode dust to acetic acid-modified and KOH-modified carbon adsorbat. Modified and unmodified carbon anode dust samples were characterized by SEM analysis. Pore volume, pore size and surface area were determined with BET method. The prepared carbons were evaluated for their adsorption capacity of nickel ions. The experimental data were analyzed by Freundlich and Langmuir isotherms. Changes in the surface morphology, surface area properties and obtained adsorption capacity indicate that acetic acid is a better modifier than KOH. Equilibrium results showed that acetic acid modification increased the CAD adsorption capacity for Ni (II) more than KOH modification.