The role of oxygen functional groups in the adsorption of heteroaromatic nitrogen compounds

Optimization of the adsorption and desorption processes of nickel octaethylporphyrin in carbon-based adsorbents

Despite being little explored for petroporphyrins recovery from oils and bituminous shales, adsorption and desorption processes can be feasible alternatives to obtain a similar synthetic material, and to characterize their original organic materials. Experimental designs were used to analyze the effects of qualitative (e.g., type of adsorbent, solvent, and diluent) and quantitative (e.g., temperature and solid/liquid ratio) variables on the adsorptive and desorptive performance regarding nickel octaethylporphyrin (Ni-OEP) removal using carbon-based adsorbents. The evaluation variables, adsorption capacity (qe ) and desorption percentage (%desorption ) were optimized by means of the Differential Evolution algorithm. The most efficient adsorbent for removing/recovery Ni-OEP was activated-carbon coconut shell, in which dispersive π-π type and acid-base interactions were likely formed. The highest values of qe and %desorption were obtained using toluene as solvent, chloroform as diluent, 293 K as temperature, and 0.5 mg.mL-1 as solid/liquid ratio for adsorption, and a higher temperature (323 K) and lower solid/liquid ratio (0.2 mg.mL-1) for desorption. The optimization process resulted in qe of 6.91 mg.g-1 and %desorption of 35.2%. In the adsorption-desorption cycles, approximately 77% of the adsorbed porphyrins were recovered. The results demonstrated the potential of carbon-based materials as adsorbent materials for obtaining porphyrin compounds from oils and bituminous shales.

Resource recovery toward sustainability through nutrient removal from landfill leachate

This study investigated the feasibility of integrated ammonium stripping and/or coconut shell waste-based activated carbon (CSWAC) adsorption in treating leachate samples. To valorize unused biomass for water treatment application, the adsorbent originated from coconut shell waste. To enhance its performance for target pollutants, the adsorbent was pretreated with ozone and NaOH. The effects of pH, temperature, and airflow rate on the removal of ammoniacal nitrogen (NH₃-N) and refractory pollutants were studied during stripping alone. The removal performances of refractory compounds in this study were compared to those of other treatments previously reported. To contribute new knowledge to the field of study, perspectives on nutrients removal and recovery like phosphorus and nitrogen are presented. It was found that the ammonium stripping and adsorption treatment using the ozonated CSWAC attained an almost complete removal (99%) of NH₃-N and 90% of COD with initial NH₃-N and COD concentrations of 2500 mg/L and 20,000 mg/L, respectively, at optimized conditions. With the COD of treated effluents higher than 200 mg/L, the combined treatments were not satisfactory enough to remove target refractory compounds. Therefore, further biological processes are required to complete their biodegradation to meet the effluent limit set by environmental legislation. As this work has contributed to resource recovery as the driving force of landfill management, it is important to note the investment and operational expenses, engineering applicability of the technologies, and their environmental concerns and benefits. If properly managed, nutrient recovery from waste streams offers environmental and socio-economic benefits that would improve public health and create jobs for the local community.

Adsorption capacity of different types of carbon nanotubes towards metronidazole and dimetridazole antibiotics from aqueous solutions: effect of morphology and surface chemistry

The effect of surface chemistry and morphology of carbon nanotubes (CNTs) on their adsorption capacity towards dimetridazole (DTZ) and metronidazole (MNZ) antibiotics from water solutions was investigated in this work. The CNTs studied were single-walled carbon nanotubes (SWCNTs), CNTs doped with nitrogen (N-CNTs), multiwalled CNTs (MWCNTs), and MWCNTs functionalized with carboxylic groups (MWCNT-COOH). The experimental adsorption equilibrium data were best interpreted with the Redlich-Peterson (R-P) isotherm model. At T of 25 °C and pH of 7, the capacities of adsorption decreased as follows: SWCNT > MWCNT > N-CNT ≈ MWCNT-COOH, and the maximum capacities of SWCNT towards MNZ and DTZ were 101 mg/g and 84 mg/g, correspondingly. The SWCNT had the highest adsorption capacity because SWCNT presented the largest surface area, and was the only nanomaterial with a basic surface. The adsorption of both antibiotics on the CNTs was predominantly ascribed to the π-π stacking. The basic groups promoted the π-π stacking interactions and favored the adsorption capacity towards MNZ and DTZ. The capacity of SWCNT for adsorbing MNZ was lessening substantially by reducing the pH from 11 to 2, and the electrostatic interactions caused this trend. The Sheindorf-Rebuhn-Sheintuch adsorption model interpreted the data for the competitive adsorption of DTZ and MNZ on SWCNT adequately.

Electro-Fenton with peroxi-coagulation as a feasible pre-treatment for high-strength refractory coke plant wastewater: Parameters optimization, removal behavior and kinetics analysis

Electro-Fenton (EF) with peroxi-coagulation (PC) as an emerging electro-chemical advanced oxidation method has been extensively applied to treat refractory wastewater. However, the studies on the pretreatment of the raw coke plant wastewater by EF process were still lacking. In this study, a lab-scale EF system (Fe as anode and graphite as cathode) achieved the highest COD removal of 69.2% based on the preliminary experiments. The process parameters and corresponding COD removal performance were further optimized using response surface methodology (RSM) combined with Box-Behnken experimental design (BBD). The optimal conditions were obtained as: 3.2 mA cm^-2 of current density, 2 h of the reaction time and 2.6 of the initial pH value, with the COD removal reaching 70.0%. Fourier infrared (FTIR), fluorescence excitation-emmission matrix (EEM) and gas chromatography-mass spectrometry (GC-MS) also revealed the degradation behaviors of dissolved organic matters (DOMs) by characterizing their structures and compositions before and after EF pretreatment, thus greatly improving the biodegradability of the wastewater. Moreover, the EF process for COD removal well followed third-order kinetics model. These findings give helpful guidance to design, optimize and control the EF process as a favourable pretreatment for actual refractory coking wastewater in practice.

Effect of nitric acid pre-oxidation concentration on pore structure and nitrogen/oxygen active decoration sites of ethylenediamine -modified biochar for mercury(II) adsorption and the possible mechanism

Controlling of pre-oxidation conditions can effectively enhance the aimed active functional groups via promoting the oxidation and grafting reaction on biochar's surface. Here, the effect of different nitric acid pre-oxidation concentration (NAPOC) was investigated on the type and content of active oxygen-containing functional sites during the pre-oxidation stage, as well as the active nitrogen-containing binding sites for the following grafting process. And the possible reaction mechanisms for introducing nitrogen/oxygen-containing functional groups such as amide, pyridinic, carbonyl, carboxyl, etc., into the surface by ethylenediamine (EDA) were proposed. The samples were characterized by various analyses including N₂ adsorption/desorption, Boehm titration, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Results showed that the NAPOC played a crucial role in promoting the formation of oxygen-containing initiators, and difference of NAPOC resulted in different reaction principles. At higher NAPOC, more carbonyl, carboxyl and hydroxyl functional groups were formed, which facilitated the decoration of nitrogen binding active sites of amide and pyridinic for mercury ions adsorption into the carbon lattice of mesoporous biomass-derived biochar (MBB). The proportions of micropore and mesopore remained basically unchanged, indicating that the decorated nitrogen/oxygen sites were highly uniformly dispersed in MBB's frame and thus resulted in high activity. The comparison of adsorption properties of MBB showed that MBB-25-EDA had the highest adsorption capacity of 153 mg g^-1 at pH 6, confirming that the 25% was the optimum NAPOC for introducing nitrogen/oxygen functional binding sites for effectively anchoring mercury.

Characterization of potassium hydroxide modified anthracite particles and enhanced removal of 17α-ethinylestradiol and bisphenol A

Anthracite is a natural inorganic-organic hybrid environmentally friendly material, which often is used as a filter medium in water treatment. In this study, we processed anthracite particles using potassium hydroxide (KOH) with different concentrations. The anthracites, before and after treatments, were characterized by Brunauer-Emmett-Teller analysis, scanning electron microscopy, Fourier transform infrared spectrometer, X-ray diffraction, X-ray photoelectron spectroscopy, and Boehm titration. The specific surface area and the amount of total alkalinity of anthracite were 23.73 m² g^-1 and 0.38 mmol g^-1 (increased by 101 and 217%, respectively) for 4 M KOH treatments, but decreased to 10.09 m² g^-1 and 0.12 mmol g^-1 for 10 M KOH treatments. We selected 4 M KOH-modified anthracite particles to remove 17α-ethinylestradiol (EE2) and bisphenol A (BPA) from water with unmodified anthracite used in control experiments. The pseudo-second-order model fitted well for the whole adsorption process, and intraparticle diffusion was not the unique rate-controlling step. The equilibrium adsorption data fitted well with the Langmuir-Freundlich model, and the adsorption capacities of EE2 and BPA on anthracite particles after 4 M KOH treatments were 0.7914 and 0.4327 mg g^-1 (increased by 138 and 97%, respectively), because the active sites markedly increased. The ligand exchange, hydrogen bonds, and π-π electron donor-acceptor interactions were the main adsorption mechanisms. The 4 M KOH-modified anthracite could be promising in large-scale applications, both as filter medium and adsorbent for organic contaminants.

Enhanced activation of periodate by iodine-doped granular activated carbon for organic contaminant degradation

In this study, iodine-doped granular activated carbon (I-GAC) was prepared and subsequently applied to activate periodate (IO₄^-) to degrade organic contaminants at ambient temperature. The physicochemical properties of GAC and I-GAC were examined using scanning electron microscopy, N₂ adsorption/desorption, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. No significant difference was observed between the two except for the existence of triiodide (I₃^-) and pentaiodide (I₅^-) on I-GAC. The catalytic activity of I-GAC towards IO₄^- was evaluated by the degradation of acid orange 7 (AO7), and superior catalytic performance was achieved compared with GAC. The effects of some influential parameters (preparation conditions, initial solution pH, and coexisting anions) on the catalytic ability were also investigated. Based on radical scavenging experiments, it appeared that IO₃ was the predominant reactive species in the I-GAC/IO₄^- system. The mechanism underlying the enhanced catalytic performance of I-GAC could be explained by the introduction of negatively charged I₃^- and I₅^- into I-GAC, which induced positive charge density on the surface of I-GAC. This accelerated the interaction between I-GAC and IO₄^-, and subsequently mediated the increasing generation of iodyl radicals (IO₃). Furthermore, a possible degradation pathway of AO7 was proposed according to the intermediate products identified by gas chromatography-mass spectrometry.

Adsorptive Removal of Nitrogen and Sulfur Containing Compounds by SBA15 Supported Nickel (II) and Tungsten Phosphides and the Adsorption Mechanisms

SBA15 supported transition metal phosphides Ni2P/SBA15 and WP/SBA15 have been identified as promising adsorbents especially for removing neutral nitrogen-containing compounds. Adsorption of model nitrogen- and sulfur-containing compounds as well as light cycled oil (LCO) was performed and applied for the evaluation of kinetics and isotherms. The pseudo second-order kinetic model was well fitted to both nitrogen and sulfur adsorption data. Molecular size of the adsorbates plays an important role in the adsorption. Despite of higher initial adsorption rates, the adsorption capacities for carbazole and DBT were lower than those for indole and quinoline due to their larger molecular size. Monolayer adsorption was observed for quinoline due to the acid-base interaction between the basic nitrogen adsorbate and the weak acidic support. The Freundlich model was suitable in describing the adsorption of nitrogen- and sulfur-containing compounds from LCO. Cooperative adsorption took place when replacing the model compound DBT by the sulfur-containing compounds in LCO.