Removal Mechanisms of Cr(VI) By Redox-Active Moieties on HNO3 Modified Biochar Under Different pH and O2 Conditions

Nitric acid (HNO3) modified biochar (NBC) has been demonstrated to be a promising sorbent. However, the roles of their redox-active moieties (RAMs, i.e., environmentally persistent free radicals (EPFRs) and oxygen-containing function groups) in Cr(VI) removal under varying pH and O2 conditions remain poorly understood. In this study, HNO3 oxidation caused an obvious increase in specific surface area, porous volume, RAMs content, and surface potential of the biochar, leading to the more effective removal of Cr(VI) (with the removal rate reached 100% at pH 2.0) than that of the untreated biochar. Kinetics experiments revealed that O2 and pH are of great importance for the reduction efficiency and rate of Cr(VI). RAMs on NBC can either directly reduce Cr(VI)(predominant pathway) or activate O2 to produce •O2− for indirect Cr(VI) reduction. In addition, we examined the changes in the compositions of RAMs during the reaction by tuning the RAMs compositions using methanol and hydrogen peroxide. The results of electron paramagnetic resonance and X-ray photoelectron spectroscopy analysis demonstrated that the main electron donors on NBC were different at different pH values: oxygen-containing groups, e.g., –OH and C–O–C, played a dominant role in reducing Cr(VI) under acidic conditions while the neutral condition was beneficial to EPFRs-dominated reduction. This study investigated the roles of the EPFRs and oxygen-containing function groups on HNO3 modified biochar, which may provide new insights into the promoted reduction of Cr(VI) by applications of biochar.

Ammonia CI engine aftertreatment systems design and flow simulation

Investigation of exhaust emissions and ammonia flow behavior in the exhaust system incorporating with Selective Catalytic Reduction (SCR) unit is discussed. An aftertreatment system is designed to work without additional urea injection to improve feasible temperature of operating and reduce size. This study is focused on obtaining optimal parameters for catalysis using gaseus ammonia as reducing agent. Its effectiveness is considered as a function of basic parameters of exhaust gases mixture and SCR material characteristics. A 3D geometry of SCR with porous volume has been simulated using Ansys Fluent. Moreover, a 1D model of ammonia dual-fuel CI engine has been obtained. Results were focused on obtaining local temperature, velocity, and exhaust gases composition to predict optimal probes placement, pipes insulation parameters, and characteristic dimensions.

Determination of the pressure inside pores

Determination of the porosity, structural characteristics of pores, and gas pressure in closed pores is the most important part of assessing physical and mechanical properties of materials. The internal pressure inside the pore can be used in estimating the level of strength reliability of the porous volume of the product to optimize the technological processes of product manufacturing, control their structure and properties, and avoid the formation of cracks at the boundaries of the particles consisting the material. We present a method for calculating the internal pressure in a spherical pore that has arisen in the material of a product obtained using powder metallurgy or additive technologies. The proposed procedure for measuring internal pressure in a pore consists in application of an external pressure to the product, measurements of the displacements of the points on the pore surface, and calculation of the internal pressure from the difference between the displacements. In this case, the known solutions of the problem of the theory of elasticity regarding the deformation of a spherical cavity located in the center of a spherical hollow ball are used. The results obtained can be used to assess the properties and structure of the products obtained by additive technology and methods of powder metallurgy, as well as to improve the technology of their manufacture.

Synthesis of Hierarchical MOR-Type Zeolites with Improved Catalytic Properties

Hierarchical MOR-type zeolites were synthesized in the presence of hexadecyltrimethylammonium bromide (CTAB) as a porogen agent. XRD proved that the concentration of CTAB in the synthesis medium plays an essential role in forming pure hierarchical MOR-type material. Above a CTAB concentration of 0.04 mol·L−1, amorphous materials are observed. These hierarchical mordenite possess a higher porous volume compared to its counterpart conventional micrometer crystals. Nitrogen sorption showed the presence of mesoporosity for all mordenite samples synthesized in the presence of CTAB. The creation of mesopores due to the presence of CTAB in the synthesis medium does not occur at the expense of zeolite micropores. In addition, mesoporous volume and BET surface seem to increase upon the increase of CTAB concentration in the synthesis medium. The Si/Al ratio of the zeolite framework can be increased from 5.5 to 9.1 by halving the aluminum content present in the synthesis gel. These synthesized hierarchical MOR-type zeolites possess an improved catalytic activity for n-hexane cracking compared to large zeolite crystals obtained in the absence of CTAB.

Guided Crystallization of Zeolite Beads Composed of ZSM-12 Nanosponges

The direct route using a bifunctional amphiphilic structuring agent for the synthesis of hierarchical nanozeolites coupled with pseudomorphic transformation was used for the crystallization of hierarchized zeolite beads/hollow spheres composed of ZSM-12 (MTW structural-type) with nanosponge morphology. These beads/hollow spheres have the same average diameter of 20 µm as their counterpart amorphous mesoporous silica beads used as precursor in the starting synthesis mixture. The effects of synthesis parameters, such as stirring and treatment time at 140 °C, on the morphology, structure, and texture of the materials have been investigated using X-ray diffraction (XRD), N2 sorption, scanning electronic microscopy (SEM), and transmission electronic microscopy (TEM) techniques. Static conditions were found necessary to maintain the morphology of the starting amorphous silica beads. An Ostwald ripening phenomenon was observed with the increase in hydrothermal treatment time leading to the dissolution of the interior of some beads to form core shell beads or hollow spheres with larger crystals on the outer surface. These ZSM-12 beads/hollow spheres possess higher porous volume than conventional ZSM-12 zeolite powder and can be used directly for industrial applications.

Influence of the Porous Volume in the Structure of Resin Bond Composite Abrasives by its Mechanical Performance

Abrasive tools consist of abrasive grains, binder and pores. Binders are the matrix of the material and may be of the metallic, vitrified or resin type. The wide use of polymeric materials (resinoid) is due to their low cost and excellent mechanical properties. The grain has the function of roughing the material, the binder, on the other hand, has the characteristics of ensuring grain adhesion and the pores in the structure are responsible for cooling the abrasive tool. In this work, we report the preparation and evaluation of the mechanical characteristics of resin bond composite abrasives with different structures based on the porous concentration. The composite abrasives were made with phenolic resin and alumina grains. Four different structures were studied from 10 to 30% of porous volume fraction with 50% of grain volume fraction. The concentration of porous and bond in the structure composition were employed to compare the mechanical performance of the prepared composite abrasive. To evaluate the mechanical properties of composites, Impact strength, Young’s Modulus by impulse excitation and flexural strength were realized. It was observed that as the porosity is higher, the impact resistance (absorbed energy) is lower, which confirms the lower resistance produced by the surface area contact (grain/binder) and a greater accumulation of tension in the binder material, the higher porosity value, higher the flexural strength value until 20% of porosity. Samples with higher volumes level of porosity presented lower Young’s Modulus but the presence of pores produced by volatiles by-products (mainly water) should act as stress concentrators, thus favoring lower mechanical properties at the resin-grain interface.

Synthesis of High Quality Porous Carbon from Water Hyacinth

Water Hyacinth (WH) is a plant that can absorb various pollutants in water. However, this plant is categorized as an invasive plant that can become a weed in the waters. To improve the functionality of WH, processing of WH is needed to be used for various applications. One of modifications of WH is as porous carbon for battery cathode composite. In this paper, we reported a synthesis of a porous carbon from WH. WH is processed into carbon by carbonization at various temperatures of 400, 500 and 600 °C with various activators of KOH, H3PO4 and ZnCl2 to obtain high quality porous carbon which has high electrical conductivity, large specific surface area and large porous volume. All synthesized carbons were characterized by proximate analysis measurements, scanning electron microscopy (SEM), and N2 adsorption-desorption measurements. The highest carbon fixed content of 37.79% is obtained from charcoal with a carbonization temperature of 400 °C. The largest specific surface area of 264.77 m2/g was obtained from activated carbon with H3PO4 as activator. The values of pore volume and pore radius were 0.186 cm3/g and 1.56 nm, respectively.

Study of the Structure and Properties of Carbon Gels from Abies Lignin and Tannins

Carbon tannin-lignin-formaldehyde (TLF) gels were obtained for the first time by carbonization of organic xerogels synthesized by sol-gel condensation of formaldehyde with polyphenolic substances isolated from abies wood and bark – ethanol lignin and condensed tannins. The effect of the mass ratio of the tannins/lignin (T/L) components in the range 1:0 – 1:2 on the specific surface areas, porous volume, apparent density, and microstructure of carbon tannin-lignin-formaldehyde gels has been studied. It was found that the density of the carbon gels increases from 0.52 to 0.60 g/cm3 with a rises in the T/L ratio from 1:0 to 1:0.2 and 1:0.5 in the initial gel and then decreases to 0.20 and 0.13 g/cm3 with an increase in the lignin content to T/L ratios of 1:1 and 1:2, respectively. The study of the porous structure of carbon gels by the BET method showed that the carbon TLF gel obtained at a T/L ratio 1:2 is characterized by the highest specific surface area (538 m2/g). Using scanning electron microscopy, the structures of TF and TLF carbon gels have been studied. It has been established that the size of globular particles has a decisive influence on the structure of gels. The size of the globule particles increases with increasing of lignin content in the composition of the tannin-lignin-formaldehyde gel that leads to the formation of a less ordered structure of the carbon gel. The porous structure of TLF carbon gels obtained from abies polyphenolic substances can be regulated by varying the ratio of tannins:lignin. The obtained carbon gels can be used as sorbents and catalyst supports