Active carbons prepared by chemical activation of plum stones and their application in removal of NO2

The low-temperature NO2 removal by tailoring metal node in porphyrin-based metal-organic frameworks

Nitrogen dioxide (NO₂) is the most toxic and prevalent form of nitrogen oxides (NO_x) pollutant and its removal from ambient air is a pressing challenge. The state-of-the-art deNO_x technologies such as selective catalytic reduction (SCR) can only work at elevated temperatures (>250-300 °C), but ineffective for the NO_x removal under ambient conditions. The adsorptive removal of NO₂ is an alternative approach to SCR, whose success depends on the design of stable adsorbents capable of selectively capturing NO₂ with a highly reversible capacity. Here we synthesized and developed five porphyrin-based metal-organic frameworks (PMOFs) as robust ambient NO₂ adsorbents, including three aluminum-based (Al-PMOF) isostructures, and two zirconium-based (Zr-PMOFs) isostructures. Of them, Al-PMOF stands out to be the most promising candidate by showing the highest NO₂ adsorption capacity (1.85 mmol/g), high stability, and good regenerability (retaining 87% capacity after five cycles of adsorption) at dry conditions. The NO₂ adsorption capacity of Al-PMOF was approximately doubled (3.61 mmol/g) at wet conditions. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed the NO₂ adsorption mechanism - the hydrogen bonding occurs between bridging hydroxyl (-OH) (attached to the metal node) and NO₂ molecules. Our work demonstrates that PMOFs are promising NO₂ adsorbents and will provide guidance for designing robust and reusable adsorbents for efficiently removing NO₂ at ambient temperature.

Activated Bio-Carbons Prepared from the Residue of Supercritical Extraction of Raw Plants and Their Application for Removal of Nitrogen Dioxide and Hydrogen Sulfide from the Gas Phase

The waste materials left after supercritical extraction of hop cones and marigold flowers were tested as precursors of activated bio-carbons. Adsorbents were produced by means of the physical (also called thermal) activation method using CO₂ as the gasifying agent. All the activated bio-carbons were tested for the removal of NO₂ and H₂S from the gas phase under dry and wet conditions. The effects of the type of precursor and the activation procedure on the porous structure development, the acid-base properties of the surface, as well as the sorption capacities of the materials produced were also checked. The final products were bio-carbons of medium developed surface area with a basic surface nature, characterized by their high effectiveness in removal of gas pollutants of acidic character, especially nitrogen dioxide (sorption capacities in the range from 12.5 to 102.6 mg/g). It was proved that the toxic gas removal efficiency depends considerably on the sorption conditions and the activation procedure. All materials showed greater effectiveness in gas removal when the process of adsorption was carried out in the presence of steam.

The Utilization of Plum Stones for Pellet Production and Investigation of Post-Combustion Flue Gas Emissions

Agri-food waste is generated at various food cycle stages and is considered to be a valuable feedstock in energy systems and chemical syntheses. This research identifies the potential and suitability of a representative agri-food waste sample (i.e., plum stones) as a solid fuel. Ground plum stones containing 10, 15, and 20 wt.% of rye bran were subjected to pelletization. The pelletizer was operated at 170, 220, and 270 rpm, and its power demand for the mixture containing 20 wt.% of rye bran was 1.81, 1.89, and 2.21 kW, respectively. Such pellets had the highest quality in terms of their density (814.6 kg·m−3), kinetic durability (87.8%), lower heating value (20.04 MJ·kg−1), and elemental composition (C: 54.1 wt.%; H: 6.4 wt.%; N: 0.73 wt.%; S: 0.103 wt.%; Cl: 0.002 wt.%; O: 38.2 wt.%). Whole plum stones and pellets were subjected to combustion in a 25 kW retort grate boiler in order to determine the changes in the concentrations of NO, SO2, CO, CO2, HCl, and O2 in the post-combustion flue gas. Collected results indicate that plum stone–rye bran pellets can serve as effective substitutes for wood pellets in prosumer installations, meeting the Ecodesign Directive requirements for CO and NO.

CO2 and CH4 Adsorption Behavior of Biomass-Based Activated Carbons

The aim of the present work is to study the effect of different activation methods for the production of a biomass-based activated carbon on the CO 2 and CH 4 adsorption. The influence of the activation method on the adsorption uptake was studied using three activated carbons obtained by different activation methods (H 3 PO 4 chemical activation and H 2 O and CO 2 physical activation) of olive stones. Methane and carbon dioxide pure gas adsorption experiments were carried out at two working temperatures (303.15 and 323.15 K). The influence of the activation method on the adsorption uptake was studied in terms of both textural properties and surface chemistry. For the three adsorbents, the CO 2 adsorption was more important than that of CH 4 . The chemically-activated carbon presented a higher specific surface area and micropore volume, which led to a higher adsorption capacity of both CO 2 and CH 4 . For methane adsorption, the presence of mesopores facilitated the diffusion of the gas molecules into the micropores. In the case of carbon dioxide adsorption, the presence of more oxygen groups on the water vapor-activated carbon enhanced its adsorption capacity.

Caveats and technical challenges in performance evaluation of activated carbon (AC) and non-AC filtration for NO2 abatement toward energy-efficient and healthy ventilation

As the awareness of public health/safety becomes important and the desire to provide clean/safe indoor air in a sustainable way increases, air filtration technology has become essential at urban built facilities, which are challenged by significant outdoor air pollution due to dense population and heavy traffic. To provide comparable/objective data for designers and professionals of gas-phase filtration equipment in HVAC systems, it is important to understand the performance and characteristics of possible filter medium candidates within a reasonable testing period at low levels of target hazard concentration (typically, ∼0.05 ppm). The present study investigated the 2000-time scale-down evaluation evidence and its behind reasons between practical high-concentration tests (∼100 ppm NO₂) and actual low-concentration ones, and investigated potential dangers identified during the study in utilizing activated carbon (AC)-based virgin filter media in indoor applications due to unexpected NO-desorption phenomenon. Six filter media of AC-based and non-AC with different type/pellet/shape/size/target compound were selected and tested for abating NO₂ mainly originated outdoors. A multi-channel simultaneous testing system was utilized for similar standard testing conditions. The study findings provide previously unavailable experimental data and new insight into the behavior of widely used filtration media against NO₂ for the enhancement of urban resilience.

Factors Influencing NO₂ Adsorption/Reduction on Microporous Activated Carbon: Porosity vs. Surface Chemistry

The textural properties and surface chemistry of different activated carbons, prepared by the chemical activation of olive stones, have been investigated in order to gain insight on the NO₂ adsorption mechanism. The parent chemical activated carbon was prepared by the impregnation of olive stones in phosphoric acid followed by thermal carbonization. Then, the textural properties and surface chemistry were modified by chemical treatments including nitric acid, sodium hydroxide and/or a thermal treatment at 900 °C. The main properties of the parent and modified activated carbons were analyzed by N₂-adsorption, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) techniques, in order to enlighten the modifications issued from the chemical and thermal treatments. The NO₂ adsorption capacities of the different activated carbons were measured in fixed bed experiments under 500 ppmv NO₂ concentrations at room temperature. Temperature programmed desorption (TPD) was applied after adsorption tests in order to quantify the amount of the physisorbed and chemisorbed NO₂. The obtained results showed that the development of microporosity, the presence of oxygen-free sites, and the presence of basic surface groups are key factors for the efficient adsorption of NO₂.

Production of new activated bio-carbons by chemical activation of residue left after supercritical extraction of hops

A technology of activated bio-carbons production from the residue left after supercritical extraction of hops is described. The effect of the variant of chemical activation and impregnation ratio on the physicochemical properties as well as sorption capacity towards toxic gas of acidic character (nitrogen dioxide), basic organic dye (aqueous solution of methylene blue - MB) and iodine was investigated. The materials obtained were activated bio-carbons of well-developed surface area ranging between 897 and 1095m²/g, showing clearly acidic character of the surface. The sorption tests results proved that chemical activation of the residue left after supercritical extraction of hops allows obtaining activated bio-carbons with very high sorption capacity towards nitrogen dioxide, reaching to 77.2 and 155.3mg/g in dry and wet conditions, respectively. The maximum sorption capacity of the adsorbents towards methylene blue was 328.75mg/g, while towards iodine 1815mg/g. The equilibrium data for aqueous solution of MB were analyzed by the Langmuir and Freundlich models, whereas the kinetics of the adsorption process was studied using pseudo-first and second-order models. According to the obtained data, the adsorption of MB from aqueous solution is better described by Langmuir model and pseudo-second order kinetic model.

Characterization of coal gasification slag-based activated carbon and its potential application in lead removal

Highly porous activated carbons were prepared from a coal gasification slag (CGS) precursor, by KOH activation to remove Pb²⁺ from aqueous solution. The effects of pretreatment methods and activation parameters on the properties of the activated carbon were investigated, such as KOH/CGS mass ratio, activation temperature and activation time. The results showed that the maximum Brunauer-Emmett-Teller surface area and total pore volume with the value of 2481 m² g^-1 and of 1.711 cc g^-1 were obtained at a KOH/CGS ratio of 3.0 by physical mixing, an activation temperature of 750°C and an activation time of 80 min. SEM, FTIR and EA analyses indicated that pronounced pores existed on the exterior surface of the activated samples, and the contents of H and O decreased due to the loss of surface chemical groups during activation. Experimental data for the Pb²⁺ adsorption were fitted well by Freundlich equation and a pseudo-second-order model with a maximum experimental adsorption capacity of 141 mg/g. All of the results indicated that CGS could be a promising material to prepare porous activated carbon for Pb²⁺ removal from wastewater.

Adsorption of Carbon Dioxide onto Activated Carbon Prepared from Coconut Shells

This study presents the fabrication of high-quality activated carbon (AC) from discarded coconut shells. The effects of experimental parameters such as activation temperature and activation time on the basic characteristics of AC, including charcoal yield, ash content, pH value, Brunauer-Emmett-Teller (BET) specific surface area, total pore volume, and iodine adsorption, are investigated. The results indicate that as the activation temperature and activation time increase, the charcoal yield of the AC decreases. In contrast, iodine adsorption, ash content, pH value, and total pore volume increase with activation temperature. The AC sample activated at 1000°C for 120 min had the highest BET specific surface area and total pore volume and thus the best CO2adsorption performance. This sample was compared with 30-mesh commercial AC. The results reveal that coconut-based AC has better instantaneous adsorption capabilities.

Activated Carbon Prepared from Date Pits for the Retention of NO2 at Low Temperature

Activated carbons were prepared from date pits by physical activation with CO2 and the textural properties were investigated by BET and D-R methods with N2 and CO2 adsorption isotherms. The interaction of the NO2 with activated carbon was examined at ambient temperature and the effect of operating conditions such as temperature and inlet gas compositions was also examined. It was observed that the development of porosity with increasing time of activation favours the adsorption capacity of NO2. The maximum adsorption capacity reached was about 107 mg/g, which is higher than several activated carbon prepared from classical lignocellulosic biomass. However, a slight decrease of NO2 adsorption capacity was observed with increasing temperature. The addition of oxygen into the inlet gas gave rise to an increase in amount adsorbed of NO2.

An amperometric NO2 sensor based on La10Si5NbO27.5 electrolyte and nano-structured CuO sensing electrode

A novel amperometric-type NO2 sensor based on La10Si5NbO27.5 (LSNO) electrolyte and nano-structured CuO sensing electrode was fabricated and tested. A bilayer LSNO electrolyte including both a dense layer and a porous layer was prepared by conventional solid state reaction method and screen-printing technology. The nano-structured CuO sensing electrode was in situ fabricated in LSNO porous layer by impregnating method. The composition and microstructure of the sample were characterized by XRD and SEM, respectively. The results showed that the CuO particles with diameters range of 200-500 nm were homogeneously dispersed on the LSNO backbone in porous layer. The sensor exhibited well sensing characteristics to NO2. The response current was almost linear to NO2 concentration in the range of 25-500 ppm at 600-800 °C. With increase of operating temperature, the sensitivity increased and reached 297 nA/ppm at 800 °C. The response currents toward NO2 were slightly affected by coexistent O2 (0-21 vol%) and CO2 (0-5 vol%).

Highly Porous Carbon Materials from Biomass by Chemical and Carbonization Method: A Comparison Study

Porous carbon obtained by dehydrating agent, concentrated sulfuric acid (H2SO4), from biomass containing high cellulose (filter paper (FP), bamboo waste, and empty fruit bunches (EFB)) shows very high surface area and better thermal behavior. At room temperature (without heating), treatment of H2SO4removed all the water molecules in the biomass and left the porous carbon without emitting any gaseous byproducts. Brunauer-Emmett-Teller (BET) surface analysis has shown that bamboo-based carbon has good properties with higher surface area (507.8 m2/g), micropore area (393.3 m2/g), and better thermal behavior (compared to FP and EFB) without any activation or treatment process. By acid treatment of biomass, it was shown that higher carbon composition obtained from FP (85.30%), bamboo (77.72%), and EFB (76.55%) is compared to carbon from carbonization process. Under optimal sulfuric acid (20 wt.%) uses, high carbon yield has been achieved for FP (47.85 wt.%), bamboo (62.4 wt.%), and EFB (55.4 wt.%).

The effect of chemical activation method on properties of activated carbons obtained from pine cones

A method for obtaining carbonaceous adsorbents from pine cones by chemical activation with NaOH is described. Activated carbons were obtained by two methods of activation (physical mixing and impregnation) and two variants of thermal treatment. It has been shown that pine cones can be successfully used as cheap precursor of carbonaceous adsorbents of well-developed surface area, large pore volume and good sorption properties. All activated carbon samples obtained show strongly microporous structure and surface of acidic character. The best physicochemical properties and greatest sorption capacity towards iodine were found for the carbon samples obtained by physical mixing of the precursor with the activating agent and then subjected to thermal activation at 600°C.

Gas nanosensor design packages based on tungsten oxide: mesocages, hollow spheres, and nanowires

Achieving proper designs of nanosensors for highly sensitive and selective detection of toxic environmental gases is one of the crucial issues in the field of gas sensor technology, because such designs can lead to the enhancement of gas sensor performance and expansion of their applications. Different geometrical designs of porous tungsten oxide nanostructures, including the mesocages, hollow spheres and nanowires, are synthesized for toxic gas sensor applications. Nanosensor designs with small crystalline size, large specific surface area, and superior physical characteristics enable the highly sensitive and selective detection of low concentration (ppm levels), highly toxic NO(2) among CO, as well as volatile organic compound gases, such as acetone, benzene, and ethanol. The experimental results showed that the sensor response was not only dependent on the specific surface area, but also on the geometries and crystal size of materials. Among the designed nanosensors, the nanowires showed the highest sensitivity, followed by the mesocages and hollow spheres-despite the fact that mesocages had the largest specific surface area of 80.9 m(2) g( - 1), followed by nanowires (69.4 m(2) g( - 1)), and hollow spheres (6.5 m(2) g( - 1)). The nanowire sensors had a moderate specific surface area (69.4 m(2) g( - 1)) but they exhibited the highest sensitivity because of their small diameter (∼5 nm), which approximates the Debye length of WO(3). This led to the depletion of the entire volume of the nanowires upon exposure to NO(2), resulting in an enormous increase in sensor resistance.

Effect of reduction treatment on copper modified activated carbons on NO(x) adsorption at room temperature

Activated carbon was impregnated with copper salt and then exposed to reductive environment using hydrazine hydrate or heat treatment under nitrogen at 925 °C. On the obtained samples, adsorption of NO(2) was carried out at dynamic conditions at ambient temperature. The adsorbents before and after exposure to nitrogen dioxide were characterized by X-ray diffraction (XRD), thermal analysis, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS), N(2)-sorption at -196 °C, and potentiometric titration. Copper loading improved the adsorption capacity of NO(2) as well as the retention of NO formed in the process of NO(2) reduction on the carbon surface. That improvement is linked to the presence of copper metal and its high dispersion on the surface. Even though both reduction methods lead to the reduction of copper, different reactions with the carbon surface take place. Heat treatment results in a significant percentage of metallic copper and a reduction of oxygen functional groups of the carbon matrix, whereas hydrazine, besides reduction of copper, leads to an incorporation of nitrogen. The results suggest that NO(2) mainly is converted to copper nitrates although the possibility to its reduction to N(2) is not ruled out. A high capacity on hydrazine treated samples is linked to the high dispersion of metallic copper on the surface of this carbon.