Impregnation Of Metal Oxides Research Articles

Tailoring metal-impregnated biochars for selective removal of natural organic matter and dissolved phosphorus from the aqueous phase

This study aimed to investigate how the production process of metal impregnated biochars (MIBs) affects their selectivity in the simultaneous adsorption of organic matter and dissolved phosphorus from the aqueous phase. MIBs were produced via a two-step pyrolysis procedure including impregnation of metal oxides in the structure of the softwood-derived biochars, resulting in copper-impregnated biochar (Cu-MIB) and iron-impregnated biochar (Fe-MIB). The tailoring process was conducted by optimization of pyrolysis temperature during the biochars production stage. The MIBs were characterized via advanced characterization analyses to acquire structural, elemental, and morphological properties of the adsorbent. The surface area of MIB (99 m2/g and 92 m2/g for Cu-MIB and Fe-MIB respectively) decreased compared to pristine biochar (571 m2/g), indicating a successful impregnation of metal oxide particles within the porous carbon structure. The effect of operational parameters on adsorption as well as selectivity tests were examined in the batch mode. The optimum doses for NOM removal were 2 g/l for Fe-MIB (96%) and 0.5 g/l for Cu-MIB (87%). For phosphorus removal, optimum doses were 1 g/l for Fe-MIB (95%) and 2 g/l for Cu-MIB (93%). The lower pH values favored adsorption for both MIBs. In the binary solution of NOM and phosphorus, the NOM was selectively adsorbed by the Cu-MIB, whereas phosphorus was selectively removed by the Fe-MIB. The results provide a deeper understanding of the tailoring process of biochars for producing new biochars as selective adsorbents for specific target pollutants.

Enhancing the adsorptive capacity of carbon nanofibers by impregnation with ferric oxide for the removal of cadmium from aqueous solution

Carbon nanofibers (CNF) possess remarkable surface properties and have been used in many applications, including water treatment. They are used for the removal of many contaminants from polluted water, including heavy metals. Further research is ongoing to enhance their removal efficiency for heavy metals. Previous studies involving the impregnation of metal oxides onto carbon adsorbents have reported an increase in CNF adsorption capacity. The incorporated ferric oxide, Fe2O3, can exist in different polymorphs. In this study, CNF impregnated with 10 wt% Fe2O3 nanoparticles was studied for its capacity to remove cadmium ions (Cd2+) from water. Both raw and Fe2O3-modified CNF (Fe-CNF) were characterized using several techniques. The SEM-EDX and XRF confirmed a successful impregnation of Fe2O3, while XRD, FTIR, and TGA showed that Fe2O3 was incorporated in the form of γ-Fe2O3 (a non-toxic and biodegradable polymorph). The effect of pH, contact time, temperature, and agitation speed on Cd2+ ions removal was tested in batch-mode adsorption experiments. The results revealed that Cd2+ ions removal efficiency achieved by Fe-CNF was around 80 % within 30 min of treating of 2.0 mg/L Cd solution at pH 8, adsorbent dosage of 5 g/L, and agitation speed of 150 rpm. The sorption of Cd2+ ions followed a pseudo-second-order model, and the thermodynamic studies indicated that iron impregnation changed the adsorption mechanism from a primarily endothermic process to a more efficient exothermic physical adsorption mechanism. Furthermore, the potential to regenerate and re-use the prepared Fe-CNF was established in 3 cycles of adsorption-desorption experiments. The 79 % cadmium recovery rate from Fe-CNF indicated its potential suitability for analytical purposes. The study demonstrated the advantage of impregnating CNF with ferric oxide to enhance the removal efficiency of Cd2+ ions from an aqueous solution.

Chemically modified carbonaceous adsorbents for enhanced CO2 capture: A review

The rapidly-increasing concentration of atmospheric carbon dioxide (CO 2 ) gas has become one of the most pressing environmental concerns in recent years. CO 2 capture has become a vital technical solution to minimize environmental CO 2 emissions from various sources. The development of advanced adsorbents for effective CO 2 adsorption is a growing area that has gained significant attention in the materials science field. Hence, in this review we systematically discuss carbonaceous materials including carbon allotropes (carbon nanotubes (CNTs) and graphene oxide (GO)), carbon aerogels (CAs), biochar, polymer-derived carbons, microporous carbons, and mesoporous carbons that are extensively utilized for CO 2 uptakes. The functionalization of carbon materials that have also been reviewed here involved physical/chemical activations using activating agents (KOH, NaOH, K 2 CO 3 , and ZnCl 2 ), doping (N, O, and S), amine modification, carboxylation (-COOH), hybrid/composites formation, and metal oxide impregnation. Studies demonstrated that these all modifications play a very essential role in enhancing the CO 2 adsorption performance as compared to pristine carbons. It is well-acknowledged that the existence of extremely microporous network with ultra-high specific surface area exhibits a dominant role in enhanced CO 2 capture. Among various functionalized carbon-based adsorbents, modified porous activated carbons proved an excellent adsorbent for efficient CO 2 uptakes because of their brilliant textural properties and economical nature. Additionally, modified carbonaceous adsorbents possessed feasible isosteric heat of adsorption, excellent regeneration ability, and shows efficient selective CO 2 adsorption over N 2 . Besides, these studies also summarize future challenges and prospective research pathway that could be commenced for developing effectual adsorbent for an efficient CO 2 storage application by considering various factors. • Carbonaceous materials as adsorbents for CO 2 capture are highlighted. • Functionalization of carbon-based adsorbents for CO 2 capture has been studied. • Recyclability and selective CO 2 adsorption capacities are also discussed. • Chemical modification extensively enhanced the CO 2 adsorption capacities.

Removal of methyl orange over TiO2/polyacrylamide hydrogel

The present work describes the preparation of titanium oxide impregnated polyacrylamide hydrogel (TiO2/PAM) by in-situ polymerization technique. The prepared hydrogel was characterized by fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and x-ray diffraction (XRD) techniques. The physical properties (solvent content, swelling behaviour, porosity) of hydrogel were also studied by ASTM method. Further, results are revealing the formation of composite hydrogel with improved properties. Thus, obtained prepared hydrogel was used for removal of methyl orange dye from laboratory prepared water samples. The methyl orange removal efficiency and kinetics was evaluated by UV-Visible spectroscopy in different conditions. The results indicate the improvement in dye removal capacity due to impregnation of metal oxides in hydrogel matrix.

Chemical activation of biochar for energy and environmental applications: a comprehensive review

Abstract Biochar (BC) generated from thermal and hydrothermal cracking of biomass is a carbon-rich product with the microporous structure. The graphene-like structure of BC contains different chemical functional groups (e.g. phenolic, carboxylic, carbonylic, etc.), making it a very attractive tool for wastewater treatment, CO2 capture, toxic gas adsorption, soil amendment, supercapacitors, catalytic applications, etc. However, the carbonaceous and mineral structure of BC has a potential to accept more favorable functional groups and discard undesirable groups through different chemical processes. The current review aims at providing a comprehensive overview on different chemical modification mechanisms and exploring their effects on BC physicochemical properties, functionalities, and applications. To reach these objectives, the processes of oxidation (using either acidic or alkaline oxidizing agents), amination, sulfonation, metal oxide impregnation, and magnetization are investigated and compared. The nature of precursor materials, modification preparatory/conditions, and post-modification processes as the key factors which influence the final product properties are considered in detail; however, the focus is dedicated to the most common methods and those with technological importance.

Comparison of the nickel addition patterns on the catalytic performances of LaCoO3 for low-temperature CO oxidation

Effect of nickel on the catalytic performances of LaCoO3 for CO oxidation is investigated, by partial substitution of Co with Ni atoms in the framework or by deposition of NiO on the surface of LaCoO3. Results show that the activity decreases in order of 10% Ni/LaCoO3>LaCoO3>LaCo0.8Ni0.2O3, with the CO ignition temperature of 60, 110 and 140°C, respectively (reaction conditions: 0.5% CO/Ar and 7.5% O2/Ar, balanced with Ar; space velocity of 30000mLg−1h−1). Based on the characterizations such as XPS, H2-TPR, O2-TPD and CV measurements, we inferred that the high activity of 10% Ni/LaCoO3 is attributed to a synergistic effect induced by NiO and LaCoO3, and the low activity of LaCo0.8Ni0.2O3 is to the enrichment of La atoms on the surface, caused by the Ni incorporation. Long-time stability test indicates that 10% Ni/LaCoO3 is stable in the reaction, with no appreciable loss of activity within 32h. The highly active and stable activity of 10% Ni/LaCoO3 suggests that impregnation of metal oxides on the surface of perovskite can be a feasible strategy for the preparation of industrial catalyst for CO oxidation.

Simultaneous Control of Elemental Mercury/Sulfur Dioxide/Nitrogen Monoxide from Coal-Fired Flue Gases with Metal Oxide-Impregnated Activated Carbon

ABSTRACTThis research investigated the effects of transition metal oxide impregnation on the physical/chemical properties and on the multipollutant (i.e., Hg0/SO2/NO) control of a commercial coconut shell-based activated carbon. V, Mn, and Cu oxides of 5 wt% as their precursor metal hydroxides were impregnated onto the activated carbon surface. After the transition metal oxide impregnation, the surface area and pore volume of activated carbon decreased. The surface morphology of activated carbons was similar prior to and after impregnation. Mn3+/Mn4+ and Cu+/Cu2+ were shown to be the major valence states presenting in the MnOx and CuOx/CAC samples, respectively. CuOx/CAC possessed the greatest Hg0 removal efficiency of approximately 54.5% under N2 condition and 98.9% under flue gas condition, respectively at 150°C. When the gas temperature increased to 350°C, the metal oxide-impregnated activated carbon still possessed appreciable Hg0 removal, especially for CuOx/CAC. The VOx/CAC had the largest SO2 removal enhancement of approximately 28.3% at 350°C. The NO removal of raw and impregnated activated carbon was very small under flue gas condition, indicating that adsorption of NO using metal oxide-impregnated activated carbon may not be a suitable route for NO control.

Methyl mercaptan removal from gas streams using metal-modified activated carbon

Abstract In this paper, removal characteristics of methyl mercaptan (CH3SH) on virgin activated carbon and the metal-modified activated carbons (M–AC) prepared by sol–gel method were studied by using a dynamic method in a fixed bed. The detailed characterization of the catalyst has been done using Scanning electron microscope (SEM), Energy–dispersive X–ray spectrometry (EDS), X–ray photoelectron spectroscopy (XPS), and N2 adsorption/desorption techniques. The results showed that impregnation of metal oxides on the AC significantly enhanced the removal capacity of methyl mercaptan, despite a notable decrease in microporosity. The catalytic activity of different kinds of metal-containing catalysts decrease in the following sequence: Cu–AC ≈ Ni–AC > Al–AC > Fe–AC > Zn–AC. Moreover, calcinations temperature can influence the catalytic activity of the catalyst greatly. XPS results showed that the methyl mercaptan were oxidized by the catalyst. Sulfate species and methyl thiolate accumulated on the catalyst surface, which can block the pores and reduce the active sites.

Multipollutant control of Hg/SO2/NO from coal-combustion flue gases using transition metal oxide-impregnated SCR catalysts

This research investigated the effects of transition metal oxide impregnation on the physical/chemical properties and the multipollutant (i.e., Hg/SO2/NO) control of a V2O5-WO3/TiO2-SiO2 selective catalytic reduction (SCR) catalyst. Additional V, Mn, and Cu of 5wt% as their precursor metal hydroxides were impregnated onto the catalyst surface. The impregnated metal oxides presenting in nanoscales caused an increase in total surface area of catalysts. SEM images suggested that the raw and treated catalysts presenting as bean-shaped nanoparticles within 10–30nm. V4+/V5+, Mn4+, and Cu2+ were the major valence states presenting on the surface of VOx-, MnOx-, and CuOx-impregnated catalysts, respectively. Hg0 oxidation, SO2 removal, and NO reduction of the SCR catalyst can be enhanced after the metal oxide impregnation. VOx- and CuOx-impregnated catalysts had not only excellent Hg0 oxidation but also great NO reduction. However, the increase in SO2 removal after metal oxide impregnation, assumed to be partly caused from enhancing SO2–SO3 conversion, may be of concern considering the potential downstream corrosion. Langmuir–Hinshelwood model can successfully explain the Hg0 oxidation by VOx- and MnOx-impregnated catalysts. Overall, multipollutant emission control using surface-impregnated SCR catalysts can be practically applied at 350°C under the tested coal-combustion flue gas condition.

Removal of SO2 over modified activated coke desulfurizers at low temperatures

A novel modified activated coke (AC) desulfurizer prepared by impregnation of metal oxides (Fe, Cu, Ni, Mn, Co), rare earth elements (Ce, La), and potassium hydroxide (KOH) was investigated. Experimental results showed that the desulfurization (DeSO2) efficiency of the ACKOH impregnation of Fe (Fe/ACKOH) was higher than other samples with impregnation of metal oxides at 120 °C and a space velocity of 8,000 h−1. At the same operating conditions, the Ce/ACKOH was more effective in two samples with impregnation of rare earth elements. As the Fe content was increased from 3 to 5 % (mass %), DeSO2 efficiency increased significantly, and kept stable at higher Fe contents (10 %). The effect of desulfurization temperature was also investigated, which revealed that, with increasing temperature from 80 to 120 °C, the DeSO2 efficiency gradually increases, while the DeSO2 efficiency decreased with increasing temperature from 120 to 140 °C.

Thick films of In, Bi and Pd metal oxides impregnated in LaCoO 3 perovskite as carbon monoxide sensor

Thick films of LaCoO 3 perovskite and metal oxides (In, Bi and Pd) impregnated in LaCoO 3 have been used as sensor materials for sensing temperature and carbon monoxide gas. LaCoO 3 has shown good characteristics of a thermal sensor up to 500 °C. The thermal sensitivity is decreased considerably by the impregnation of metal oxides and it has shown very low with PdO and Bi 2O 3. The sensor response for CO is quite good with a good recovery for the partial pressures from 10 to 40 ppm at 200 and 250 °C. LaCoO 3 has exhibited good response in spite of low sensitivity and better recovery even at 200 °C for 10 ppm partial pressure of CO. Higher partial pressures have given higher sensor responses. Probable mechanisms have been proposed in the light of present investigation and the earlier work.