Evaluation of the potential of volatile organic compound (di-methyl benzene) removal using adsorption on natural minerals compared to commercial oxides

MnO2-decorated N-doped carbon nanotube with boosted activity for low-temperature oxidation of formaldehyde

Low-temperature oxidative degradation of formaldehyde (HCHO) using non-noble metal catalysts is challenging. Herein, novel manganese dioxide (MnO₂)/N-doped carbon nanotubes (NCNT) composites were prepared with varying MnO₂ content. The surface properties and morphologies were analyzed using X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). Comparing with MnO₂/carbon nanotubes (CNTs) catalyst, the 40% MnO₂/NCNT exhibited much better activity and selectivity for HCHO oxidation, mineralizing 95% of HCHO (at 100 ppm) into CO₂ at 30 °C at a gas hourly space velocity (GHSV) of 30,000 mL h^-1  g^-1. Density functional theory (DFT) calculation was used to analyze the difference in the catalytic activity of MnO₂ with CNTs and NCNT carrier. It was confirmed that the oxygen on NCNT was more active than CNTs, which facilitated the regeneration of MnO₂. This resulted in remarkably boosted activity for HCHO oxidation. The present work thus exploited an inexpensive approach to enhance the catalytic activity of transition metal oxides via depositing them on a suitable support.

Efficient removal of gaseous formaldehyde by amine-modified diatomite: a combined experimental and density functional theory study

Amine-modified diatomite with remarkable formaldehyde (HCHO) removal efficiency was prepared by grafting 3-aminopropyltrimethoxysilane (APTMS) in this research. The interfacial properties and microstructures of the prepared adsorbents were characterized and analyzed. The HCHO adsorption properties of the amine modified diatomite were also systematically studied, and it has been proven to be effective adsorbent with better adsorption performance than activated carbon for the removal of gaseous HCHO. Furthermore, to better explain the experimental results, we performed density functional theory (DFT) study on the adsorption system and calculated the geometry, energy, and charge parameters based on first principles. Also, the underlying adsorption mechanism was proposed detailedly by combining experimentation with DFT calculation, suggesting that amine modified diatomite can be efficient adsorbent for the elimination of gaseous formaldehyde.

Adsorption of volatile organic compounds onto natural porous minerals

The abundance of natural porous minerals and their low cost make them the potential adsorbents for VOCs (volatile organic compounds). In this paper, three natural minerals (diatomite, stellerite and vitric tuff) and their corresponding acid-treated minerals were used as adsorbents. The adsorption performances of minerals were investigated by the adsorption breakthrough curves of VOCs. The results indicated that the properties of organic compounds such as boiling point and polarity and the surface area and pore volume of minerals had obvious effects on the adsorption of VOCs over minerals. Increasing adsorption temperature and relative humidity would have negative effects on the VOC adsorption of minerals. The adsorption capacity of 2-heptanone over acid stellerite decreased by 7.2% as the temperature rose from 25°C to 45°C. The adsorption capacity of acid stellerite for 2-heptanone reduced by 60.9% when relative humidity increased from 0% to 75%. Minerals were tested for five adsorption-regeneration cycles to study the reusability. Better fittings of Thomas model, pseudo-first order kinetics model, and Freundlich model were showed in fitting the adsorption. Overall, porous minerals with high specific surface area and pore volume have promising prospect in VOCs adsorption.

Sorption of BTEX on a nanoporous composite of SBA-15 and a calcined hydrotalcite

Benzene, toluene, ethylbenzene, and p-xylene (BTEX) are hazardous volatile organic compounds mostly released from fuel combustion, paint gas emissions, and biomass burning. In this work, it is studied the BTEX sorption influence on the surface reactivity of a new kind of nanoporous composite, prepared via an in situ functionalization of SBA-15 with a Mg-Al calcined hydrotalcite (HT_C). During its preparation, Mg/Al mixed oxides are indeed formed and dispersed on the SBA-15 surface with non-blockage porosity. Furthermore, the physicochemical surface properties are exalted from its precursors and it is synergistically favorable for the BTEX sorption at low pressure and temperature.

Organic–inorganic hybrids having a talc-like structure as suitable hosts to guest a wide range of species

The sol–gel process involving hydrolysis and condensation reactions is an attractive way to form siloxane based hybrid materials since it is a one-step method performed under mild conditions.

Toluene removal from waste air stream by the catalytic ozonation process with MgO/GAC composite as catalyst

This paper investigates the catalytic potential of MgO/GAC composite for toluene elimination from waste air in the catalytic ozonation process (COP). The MgO/GAC composite was a micro-porous material with the BET surface area of 1082m(2)/g. Different functional groups including aromatic CC, saturated CO of anhydrates, hydroxyl groups and SH bond of thiols were identified on the surface of MgO/GAC. Effects of residence time (0.5-4s), inlet toluene concentration (100-400ppmv) and bed temperature (25-100°C) were investigated on degradation of toluene in COP. Impregnation of GAC with MgO increased the breakthrough time and removal capacity by 73.9% and 64.6%, respectively, at the optimal conditions. The catalytic potential of the GAC and MgO/GAC for toluene degradation was 11.1% and 90.6%, respectively, at the optimum condition. The highest removal capacity using MgO/GAC (297.9gtoulene/gMgO/GAC) was attained at 100°C, whereas the highest removal capacity of GAC (128.5mgtoulene/gGAC) was obtained at 25°C. Major by-products of the toluene removal in COP with GAC were Formic acid, benzaldehyde, O-nitro-p-cresol and methyl di-phenyl-methane. MgO/GAC could greatly catalyze the decomposition of toluene in COPand formic acid was the main compound desorbed from the catalyst. Accordingly, the MgO/GAC is an efficient material to catalyze the ozonation of hydrocarbon vapors.

Application of high silica zeolite ZSM-5 in a hybrid treatment process based on sequential adsorption and ozonation for VOCs elimination

In this study, a hydrophobic synthetic zeolite, namely ZSM-5 is chosen as an adsorbent/catalyst for toluene removal. Experimental results showed that toluene adsorption onto ZSM-5 was favourable, following a Langmuir adsorption isotherm model. ZSM-5 zeolite was regenerated using gaseous ozone at low temperature. Adsorbed toluene was oxidised, releasing mainly CO2 and H2O. Traces of oxidation by-products such as acetic acid and acetaldehyde were formed and remained adsorbed after the oxidativate regeneration with ozone. After four successive cycles of adsorption/ozonation, the adsorption efficiency was not affected (92%-99%). These results showed that volatile organic compound (VOC) removal by adsorption onto ZSM-5 zeolite followed by ozone regeneration could be used as a promising hybrid process for the control of VOC emissions in terms of efficiency.

Influence of activated carbon porosity and surface oxygen functionalities' presence on adsorption of acetonitrile as a simple polar volatile organic compound

Based on series of porous carbon models, systematic Monte Carlo studies on the adsorption of acetonitrile (as a simple representative of polar volatile organic compounds) were performed. The influence of porosity and chemical composition of the carbon surface on CH3CN adsorption was studied and it was shown that both the factors influenced the adsorption mechanism. A decrease in the pore size and the introduction of oxygen surface groups led to a rise in adsorption energy and to an increase in the filling of accessible volume in the low-pressure part of the isotherm. However, from a practical point of view, it is easier to increase the adsorption by introducing polar groups on the carbon surface than by modifying the porosity.

Effective ligand functionalization of zirconium-based metal-organic frameworks for the adsorption and separation of benzene and toluene: a multiscale computational study

The adsorption and separation properties of benzene and toluene on the zirconium-based frameworks UiO-66, -67, -68, and their functional analogues UiO-Phe and UiO-Me2 were studied using grand canonical Monte Carlo simulations, density functional theory, and ideal adsorbed solution theory. Remarkable higher adsorption uptakes of benzene and toluene at low pressures on UiO-Phe and -Me2 were found compared to their parent framework UiO-67. It can be ascribed to the presence of functional groups (aromatic rings and methyl groups) that significantly intensified the adsorption, majorly by reducing the effective pore size and increasing the interaction strength with the adsorbates. At high pressures, the pore volumes and accessible surfaces of the frameworks turned out to be the dominant factors governing the adsorption. In the case of toluene/benzene separation, toluene selectivities of UiOs showed a two-stage separation behavior at the measured pressure range, resulting from the greater interaction affinities of toluene at low pressures and steric hindrance effects at high pressures. Additionally, the counterbalancing factors of enhanced π delocalization and suitable pore size of UiO-Phe gave rise to the highest toluene selectivity, suggesting the ligand functionalization strategy could reach both high adsorption capacity and separation selectivity from aromatic mixtures at low concentrations.

Liquid Phase adsorption kinetics and equilibrium of toluene by novel modified-diatomite

The adsorption equilibria of toluene from aqueous solutions on natural and modified diatomite were examined at different operation parameters such as pH, contact time, initial toluene concentration was evaluated and optimum experimental conditions were identified. The surface area and morphology of the nanoparticles were characterized by SEM, BET, XRD, FTIR and EDX analysis. It was found that in order to obtain the highest possible removal of toluene, the experiments can be carried out at pH 6, temperature 25°C, an agitation speed of 200 rpm, an initial toluene concentration of 150 mg/L, a centrifugal rate of 4000 rpm, adsorbent dosage = 0.1 g and a process time of 90 min. The results of this work show that the maximum percentage removal of toluene from aqueous solution in the optimum conditions for NONMD was 96.91% (145.36 mg/g). Furthermore, under same conditions, the maximum adsorption of natural diatomite was 71.45% (107.18 mg/g). Both adsorption kinetic and isotherm experiments were carried out. The experimental data showed that the adsorption follows the Langmuir model and Freundlich model on natural and modified diatomite respectively. The kinetics results were found to conform well to pseudo-second order kinetics model with good correlation. Thus, this study demonstrated that the modified diatomite could be used as potential adsorbent for removal of toluene from aqueous solution.