Acidic Functional Group Contents Research Articles

Investigating the synergistic potential of Si and biochar to immobilize Ni in a Ni-contaminated calcareous soil after Zea mays L. cultivation

Abstract. In Iran, a significant percentage of agricultural soils are contaminated with a range of potentially toxic elements (PTEs), including Ni, which need to be remediated to prevent their entry into the food chain. Silicon (Si) is a beneficial plant element that has been shown to mitigate the effects of PTEs on crops. Biochar is a soil amendment that sequesters soil carbon and that can immobilize PTEs and enhance crop growth in soils. No previous studies have examined the potentially synergistic effect of Si and biochar on the Ni concentration in soil chemical fractions and the immobilization thereof. Therefore, the aim of this study was to examine the interactive effects of Si and biochar with respect to reducing Ni bioavailability and its corresponding uptake in corn (Zea Mays) in a calcareous soil. A 90 d factorial greenhouse study with corn was conducted. Si application levels were 0 (S0), 250 (S1), and 500 (S2) mg Si kg−1 soil, and biochar treatments (3wt %) including rice husk (RH) and sheep manure (SM) biochars produced at 300 and 500 °C (SM300, SM500, RH300, and RH500) were utilized. At harvest, the Ni concentration in corn shoots, the Ni content in soil chemical fractions, and the release kinetics of DPTA (diethylenetriaminepentaacetic acid)-extractable Ni were determined. Simultaneous utilization of Si and SM biochars led to a synergistic reduction (15 %–36 %) in the Ni content in the soluble and exchangeable fractions compared with the application of Si (5 %–9 %) and SM (5 %–7 %) biochars separately. The application of Si and biochars also decreased the DPTA-extractable Ni and Ni content in corn shoots (by up to 57 %), with the combined application of SM500 + S2 being the most effective. These effects were attributed to the transfer of Ni in soil from more bioavailable fractions to more stable iron-oxide-bound fractions, related to soil pH increase. SM500 was likely the most effective biochar due to its higher alkalinity and lower acidic functional group content which enhanced Ni sorption reactions with Si. The study demonstrates the synergistic potential of Si and SM biochar for immobilizing Ni in contaminated calcareous soils.

Enhanced Adsorption of Aqueous Pb(II) by Acidic Group-Modified Biochar Derived from Peanut Shells

Using peanut shells, a sustainable agricultural waste product, as its raw material, the acid group-modified biochar (AMBC) was prepared through phosphoric acid activation, partial carbonization, and concentrated sulfuric acid sulfonation for efficient removal of lead ion from aqueous solutions. Characterization techniques such as N2 isothermal adsorption–desorption, SEM, XRD, FT-IR, TG-DTA, and acid–base titration were utilized to fully understand the properties of the AMBC. It was found that there were high densities of acidic oxygen-containing functional groups (-SO3H, -COOH, Ph-OH) on the surface of the AMBC. The optimal adsorption performance of the AMBC for Pb(II) in water occurred when the initial concentration of Pb(II) was 100 mg/L, the pH was 5, the dosage of the adsorbent was 0.5 g/L, and the contact time was 120 min. Under the optimal conditions, the removal ratio of Pb(II) was 76.0%, with an adsorption capacity of 148.6 mg/g. This performance far surpassed that of its activated carbon precursor, which achieved a removal ratio of 39.7% and an adsorption capacity of 83.1 mg/g. The superior adsorption performance of AMBC can be caused by the high content of acidic oxygen-containing functional groups on its surface. These functional groups facilitate the strong binding between AMBC and Pb(II), enabling effective removal from water solutions.

STUDY OF NON-FUEL APPLICATION OF BROWN COAL DERIVATIVES IN THE PRODUCTION OF MEMBRANES BASED ON HYBRID BIODEGRADABLE MATERIALS

The article shows research into the non-fuel use of brown coal derivatives in the production of membranes based on hybrid biodegradable materials. The work used polylactide brand Terramac TP-4000, humic substances obtained from brown coals. Membranes for water purification from heavy metals were obtained from hybrid biopolymer materials based on pol- ylactide and humic substances in the form of polymer porous films with a pore size of 20 microns and a working surface area of the membrane of 28.26∙10-4 m2 with a circle diameter of 6 cm. Used in our The work of humic substances belonged to the group of well-hummified, more aromatic with a high content of acidic functional groups, which leads to their high com- plexing ability to form stable metal-humic complexes. The developed hybrid biodegradable materials based on polylactide and humic substances were used as highly effective sorption membrane materials to reduce the content of heavy metals in aqueous solutions. Obtaining membranes of hybrid biodegradable materials based on polylactide and humic substances have maximum selectivity for the extraction of metal ions in relation to Cu2+ – 95 % and Pb2+ – 94 %; and for metals such as Cd2+, Hg2+, Zn2+ and Co2+, it ranges from 82 to 89 %. Comparing the percentage of metal ions adsorbed, it can be seen that the easiest adsorbed metal was lead, copper and zinc adsorbed similarly, with cadmium showing the lowest percentage, but its adsorption was slightly worse than in the case of copper and zinc. The highest value was obtained for single adsorption of Cu2+ ions; in the case of adsorption from a mixture, this metal also had the highest distribution coefficient, and strong adsorption was also found for Pb2+. On the other hand, the adsorption of Zn2+ was, according to the “partition coefficient,” relatively weak. Strong and residual phases were highest for copper and lead, these two metals were largely bound into strong complexes by humic substances and only a very small amount could be washed out under normal conditions. It was found that the leaching of metal ions from mem- brane hybrid biodegradable materials based on polylactide and humic substances into water was very low, in most cases it was about 10 % and did not exceed 20 %. Most of the metal ions (≥60 %) were very tightly bound and were partially leached out under strongly acidic conditions. The obtained results of adsorption resistance vary significantly and correlate well with the age and degree of humification of humic substances.

Removal of antibiotics, bacterial toxicity, and occurrence of antibiotic resistance genes in secondary hospital effluents treated with granular activated carbon and the impact of preceding chlorination

This comprehensive investigation highlighted the complex adsorption behaviors of antibiotics onto granular activated carbon (GAC), the effectiveness of this adsorption in reducing bacterial toxicity, and the reduction of antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) in hospital wastewater (HWW) effluents. Six GACs were characterized for their physicochemical properties, and their ability to adsorb six antibiotics in the background matrix of actual HWW was evaluated. Coconut shell-derived GAC (Co-U), which had the highest hydrophobicity and lowest content of oxygen-containing acidic functional groups, demonstrated the highest adsorption capacities for the tested antibiotics. Bacterial toxicity tests revealed that GACs could eliminate the bacterial toxicity from antibiotic intermediates present in chlorinated HWW. By contrast, the bacterial toxicity could not be removed by GACs in non-chlorinated HWW due to the greater presence of intermediate components identified by LC-MS/MS. The intraparticle diffusion coefficient of antibiotics adsorbed onto Co-U could be calculated by adsorption kinetics derived from the linear driving force model and the homogenous intraparticle diffusion model associated with the linear adsorption isotherms (0–150 μg/L). Meropenem and sulfamethoxazole exhibited the highest adsorption capacities in a single-solute solution compared to penicillin G, ampicillin, cetazidime, and ciprofloxacin. However, the greater adsorption capacities of meropenem and sulfamethoxazole disappeared in mixed-solute solutions, indicating the lowest adsorption competition. GAC can eliminate most ARGs while also promoting the growth of some ARB. Chlorination (free chlorine residues at 0.5 mg Cl2/L) did not significantly affect the overall composition of ARGs and ARB in HWW. However, the accumulation of ARGs and ARB on GAC in fixed bed columns was lower in chlorinated HWW than in non-chlorinated HWW due to an increase in the adsorption of intermediates.

Efficient Adsorption of Ammonia by Surface-Modified Activated Carbon Fiber Mesh.

In view of the characteristics and risks of ammonia, its removal is important for industrial production and environmental safety. In this study, viscose-based activated carbon fiber (ACF) was used as a substrate and chemically modified by nitric acid impregnation to enhance the adsorption capacity of the adsorbent for ammonia. A series of modified ACF-based adsorbents were prepared and characterized using BET, FTIR, XPS, and Boehm titration. Isotherm tests (293.15 K, 303.15 K, 313.15 K) and dynamic adsorption experiments were performed. The characterization results showed that impregnation with low concentrations of nitric acid not only increased the surface acidic functional group content but also increased the specific surface area, while impregnation with high concentrations of nitric acid could be able to decrease the specific surface area. ACF-N-6 significantly increased the surface functional group content without destroying the physical structure of the activated carbon fibers. The experimental results showed that the highest adsorption of ammonia by ACFs was 14.08 mmol-L-1 (ACF-N-6) at 293 K, and the adsorption capacity was increased by 165% compared with that of ACF-raw; by fitting the adsorption isotherm and calculating the equivalent heat of adsorption and thermodynamic parameters using the Langmuir-Freundlich model, the adsorption process could be found to exist simultaneously. Regarding physical adsorption and chemical adsorption, the results of the correlation analysis showed that the ammonia adsorption performance was strongly correlated with the carboxyl group content and positively correlated with the relative humidity (RH) of the inlet gas. This study contributes to the development of an efficient ammonia adsorption system with important applications in industrial production and environmental safety.

Impacts of fulvic acid and Cr(VI) on metabolism and chromium removal pathways of green microalgae

Green microalgae are highly efficient and cost-effective in the removal of heavy metals from water. However, dissolved organic matter (DOM), such as fulvic acid (FA), can impact their growth and heavy metal accumulation. Nonetheless, the specific mechanisms underlying these effects remain poorly understood. This study investigated the effects of different FA concentrations on the development, metabolism, and chromium (Cr) enrichment of Chlorella vulgaris, a standard green microalga. The findings revealed that low FA concentrations alleviated Cr-induced stress, stimulated microalgal growth, and enhanced energy conservation by suppressing chlorophyll synthesis. The highest chromium enrichment and reduction rates of 38.73% and 57.95% were observed when FA concentration reached 20 mg/L of total organic carbon (TOC). Furthermore, FA facilitated chromium removal by C. vulgaris through extracellular adsorption. Examination of microalgal cell surface functional groups and ultrastructure indicated that FA increased adsorption site electrons by promoting extracellular polymeric substance (EPS) secretion and enhancing the oxygen content of acidic functional groups. As a result, FA contributed to elevated enrichment and reduction rates of Cr in microalgal cells. These findings provide a theoretical basis for the prevention and control of heavy metal pollution in water environments.

The presence of copper ions alters tetracycline removal pathway in aerobic granular sludge: Performance and mechanism

This study investigated the removal characteristics of tetracycline (TC) in the presence of copper ions (Cu2+) in aerobic granular sludge by analyzing the TC removal pathway, composition and functional group changes of extracellular polymeric substances (EPS), and microbial community structure. The TC removal pathway changed from cell biosorption to EPS biosorption, and the microbial degradation rate of TC was reduced by 21.37% in the presence of Cu2+. Cu2+ and TC induced enrichment of denitrifying bacteria and EPS-producing bacteria by regulating the expression of signaling molecules and amino acid synthesis genes to increase the content of EPS and –NH2 groups in EPS. Although Cu2+ reduced the content of acidic hydroxyl functional groups (AHFG) in EPS, an increase in TC concentration stimulated the secretion of more AHFG and –NH2 groups in EPS. The long-term presence of TC presence of the relative abundances of Thauera, Flavobacterium and Rhodobacter and improved the removal efficiency.

A novel micro-sphere activated carbon synthesized from waste cigarette butts for ammonia adsorption

Waste cigarette filters mainly contain hardly degradable cellulose acetate, toxic nicotine, and traces of heavy metals, and therefore cause environmental pollution hazards when discarded. In order to convert cigarette butt waste into a valuable product, this article investigates the preparation of activated carbon from cigarette butts via a two-step process of hydrothermal reaction and a subsequent chemical activation with phosphoric acid as an activator. During hydrothermal reaction, it was found that a process of decarboxylation and dehydration cleavage of acetate occurs, leading to micron fragments and subsequent agglomeration into carbonaceous micro-spheres. The cigarette-butts-derived activated carbon micro-spheres have a high BET surface area of ∼ 1406 m2/g and NH3 adsorption capacity of ∼ 35.9 mg/g. It was revealed that the ammonia adsorption capacity tends to be positively and linearly correlated with the acidic functional group content of the activated carbon surface while negatively with BET surface area.

Humic Acid Extracted from Danty via Catalytic Oxidation Using H2O2/Birnessite: Characteristics and Agricultural Beneficial Effects.

Extraction optimization is very important for the quality of humic acid (HA). In this study, actived HA (HAb) was extracted from danty via catalytic oxidation using birnessite as a catalyst and H2O2 as an oxidant. Single-factor experiments and the response surface method were used to optimize the acidic functional group content of HAb. It was found that the maximum acidic functional group content of HAb can be achieved when danty-crushing time, H2O2 concentration, and birnessite dose were 105.7 min, 20, and 2%, respectively. Fourier transform infrared spectra showed that HAb had more surface functional groups than commercial HA (HAc) and HA extracted using the traditional method of the International Humic Substances Society (HAI). In addition, acidic functional group titration showed that HAb had 84.3% more acidic functional groups and 118.9% more carboxyl groups than HAI. Additionally, HAb had the greatest effect on promoting the dissolution of carbonate and bicarbonate, promoting the settlement of calcaline alkaline soil, and improving the germination rate of wheat seeds under saline and alkaline stress. This study provides a basis for the efficient extraction of active HA with rich functional groups and its application in agriculture and many other fields.

Preparation of nitrogen-enriched pine sawdust-based activated carbons and their application for copper removal from the aquatic environment

In this research study, compressed pellets of pine wood sawdust were carbonized at a temperature of 600 °C and then physically activated at 800 °C to obtain activated carbons (ACs). Then, some of the samples were enriched with nitrogen by reaction with urea at 300 °C. The AC samples prepared in this way were examined for the removal of Cu(II) in adsorption processes. Pine wood sawdust is waste resulting from processing in the wood industry and is a promising material to be reused for metal ions recovery. For this purpose, firstly, the AC was characterized using several analytical methods, including ash content, elemental composition, TGA, specific surface area and pore diameter (BET), pore size distribution (BJH), micropore volume, the content of surface acidic and basic functional groups, pH, FTIR and SEM morphology. Secondly, these materials before and after modification with nitrogen were used in experiments on the adsorptive removal of Cu(II) ions from aqueous solutions. The influence of parameters, such as initial pH, adsorbent dosage, initial Cu(II) concentration and contact time on the process, was investigated. Thirdly, adsorption kinetics and sorption isotherms were analyzed. According to the research results, it was reported that maximum sorption efficiency was equal to 99.9 and 99.8% at pH 5 for activated carbon AC (TK6AF1/2) and nitrogen-modified activated carbon NMAC (TK6MAF1/2), respectively. This proves that the examined waste materials exhibit satisfactory sorption properties in relation to Cu(II) ions and can be used as low-cost adsorbents in industrial wastewater treatment processes. These studies are in line with current global trends in sustainable and circular economy. Future research may focus on performing adsorption processes of copper and other metals at various temperatures as well as dynamic flow, studying metal ion competition, performing regeneration to reuse the adsorbents, carrying out realistic wastewater studies and cost estimation of entire processes on a laboratory and industrial scale.

New possibility for characterization of dissociation behaviour of supramolecular electrolytes: results obtained for the International Humic Substances Society standard and reference samples by coulometry

BackgroundHumic substances can be considered as polyelectrolytes with supramolecular character and complicated behaviour in water environment. The fractions of humic substances dissolved in water are the most active ones and determinative for their functioning in nature, where the proton-binding and dissociation ability play a crucial role. The dissociation behaviour of humic and fulvic acids can be affected by different circumstances including their concentration which is directly connected with the molecular organization of humic particles in solution and the accessibility of their ionizable functional groups. This study is focused just on these active fractions and their dissociation behaviour in the dependence on their content in studied system.ResultsStandards and reference samples of International Humic Substances Society were used. Flow-through coulometry was used to determine the total content of acidic functional groups in fulvic solutions and humic leachates. The amount of dissociated acidic groups was determined on the basis of potentiometry. Several differences between the behaviour of humic and fulvic acids were found. While whole samples of fulvic acids including the weakest functional groups were analysed, only the active dissolved humic fractions containing stronger acidic functional groups were characterized. The fractions containing higher amounts of the weakest functional groups remained insoluble. The dissociation degree of fulvic acids decreased with their increasing content, but a maximum on its concentration dependence obtained for humic acids was observed.ConclusionsTwo different values of dissociation constants were determined for each sample. The first was determined on the basis of the extrapolation of infinite dilution, second was determined as their average value in the region of high concentrations in which it was constant. Obtained values characterize the functioning of dissolved humic substances from point of view of their dissociation ability. The results obtained by this approach can help to predict the acid–base behaviour of dissolved organic carbon in soil and generally in nature. The acid–base behaviour of dissolved organic carbon depends on its ratio to water. It behaves differently in soil which is dry and in soil which is wet or saturated by water.

CATION EXCHANGE CAPACITY OF THE HUMUS PART OF THE WEST SIBERIAN TRANSECT SOILS

The article analyzes the change in the indicator of the cation exchange capacity (CEC) in the humus of the latitudinal series of soils in Western Siberia. It is shown that not all humus substances are able to perform the function of cation exchange and participate in the formation of the organic part of the soil EC. It is shown that the organic matter in the latitudinal range of soils in Western Siberia is distributed in accordance with the known geographical pattern of the distribution of the total humus stock and the main characteristics of this stock. An unconventional evaluation method for determining the EC is proposed using analytical data on the content of acidic functional groups in humic acids and the composition of humic substances, which allows us to separately assess the contribution of humic and fulvic acids in the composition of the EC of the soil.

Purification of Aqueous Media by Biochars: Feedstock Type Effect on Silver Nanoparticles Removal.

Due to the harmful effects of nanoparticles in the environment, their effective removal from aqueous media is of great importance. This paper described the research on the silver nanoparticles (Ag-NPs) sorption on biochars obtained from different feedstock types. The sorbents were produced through pyrolysis (double-barrel method) of the vineyard (BV), paulownia tree (BP), and tobacco (BT). BV exhibited the highest specific surface area, porosity, value of variable surface charge, and content of surface acidic functional groups among the used biochars. The pseudo-second order model best described the obtained adsorption kinetics, whereas the Freundlich model accounted for the registered adsorption data. The Ag-NPs removal was highly efficient in the case of BV, especially in the nanoparticle concentration range 50–500 mg/L. Thus, this biochar can be considered as an ecofriendly, effective, low-cost organic adsorbent, potentially used in the aqueous media purification.

Kinetic and thermodynamic study of n-pentane adsorption on activated carbons modified by either carbonization or impregnation with ammonium hydroxide

Abstract This study investigates the n-pentane adsorption performances on different activated carbons both as raw and modified by means of either chemical (amination with ammonium hydroxide) or thermal (carbonization at 1273 K) treatments. The raw, chemically and physically modified activated carbons were tested for n-pentane adsorption at 261 K in a volumetric apparatus. Maximum adsorption capacity values of 13, 11.7 and 9.1 μmol g−1 were obtained for the thermally, chemically and raw activated carbons, respectively, thus testifying the effectiveness of the treatment methods in improving the n-pentane adsorption capacity of the parent sorbent, due to an increase in the content of both acidic and basic functional groups. On the other hand, at low n-pentane partial pressures the volume of ultramicropores appears the ruling faction in determining a higher sorbent capture capacity. Kinetic adsorption data were successfully modelled according to the fractal-like Vermeulen model, and the outcomes suggested a more marked time-dependence of the intraparticle diffusivity for the chemically treated sample, likely related to a greater surface heterogeneity of this sample. Immersion enthalpy data also suggested that weaker adsorbate-adsorbent interactions promote a faster diffusion process.

Facile Synthesis of Carboxylated Activated Carbon Using Green Approach for Water Treatment

A chemical treatment by using oxidizing agents is the most common methodology to modify or create functional groups on activated carbon. The modified activated carbon obtained from chemical oxidation needs further treatment and produced waste, therefore a new approach is needed. A facile green approach is reported. In this approach the activated carbon was oxidized using air without additional chemical treatment to increase the content of acidic surface functional groups, especially carboxyl groups. The formation of carboxyl groups was confirmed by Temperature Programmed Decomposition, Boehm titration, and Infra-red spectroscopy results. The Boehm titration result showed higher contents of carboxyl groups by three-fold. The carboxylated activated carbon synthesized by green approach showed excellent performance for water treatment.

Insight into the interaction mechanism of iron ions with soil humic acids. The effect of the pH and chemical properties of humic acids.

The main aim of this work was to study the mechanisms of interaction between iron(II) ions and humic acids as a function of pH, iron concentration and various humic acids chemical properties, including the degree of humification, elemental composition, aromaticity and content of acidic functional groups. The results indicated that iron was bound by humic acids at pH 7 in amounts ∼2 times higher than at pH 5 (averaged capacities: 117 and 57 cmol/kg, respectively). Iron binding at pH 7 increased with increasing the total carboxylic and phenolic groups content and the degree of humification of humic acids (R-coefficients: 0.99 and 0.95, respectively). The stability of humic acid-iron complexes at pH 7 were only slightly lower than at pH 5 due to iron hydroxides formed at pH > 5 (averaged stability constants: 5.18 and 5.26, respectively). Iron coordination mode varied depending on pH: at pH 5, the bidentate (chelate) mode dominated, whereas at pH 7 the bridging mode appeared prevalent. The total amount of bound iron was much smaller than the content of the carboxylic and phenolic groups in humic acids, on average by ∼80 (pH 7) and ∼90.1% (pH 5) indicating the occurrence of steric effects in humic acid structure i.e. the reduction of the complexation capacity of free functional groups by adjacent groups occupied by iron and/or the formation of intramolecular aggregates with iron hindering the access of further metal ions. At pH 5 the complexes were soluble in the iron concentration range positively correlated to carboxylic and phenolic groups content, showing the protective nature of negatively charged functional groups on the stability of the solution. At this pH, the destabilization of the system was governed by the neutralization of humic acid charged structures by metal cations and the compression of the double electric layer. At pH 7 the stability of the humic acid-iron solution was largely determined by the form of iron, mainly by the precipitation of metal hydroxides acting as a flocculant destabilizing the solution by co-precipitation of humic acid-iron complexes.

Effect of Chemical Oxidation on the Adsorption Properties of Cationic Dye on Activated Carbons Prepared from Locally Atropa belladonna

This study investigates the influence of wet chemical oxidation using nitric acid and ammonium persulfate on the surface nature and the adsorption properties of activated carbon prepared from sulfuric acid activation of locally Atropa belladonna plant at 200oC. The surface properties of produced carbons (AC-S, AC-S/N and AC-S/A, respectively) were demonstrated by FTIR, potentiometric titration and N2 adsorption. The adsorption properties of these carbons were estimated using methyl green (MG) dye as a cationic dye. The effect of variables including pH, initial dye concentration and contact time on the adsorption properties of these carbons was studied. Acidic carbon adsorbents were obtained with large content of acidic surface functional groups in the sequence order AC-S<AC-S/N<AC-S/A as confirmed by FTIR and potentiometric plots. It was assessed that a large number of basic functional groups were generated after oxidation with ammonium persulfate (AC-S/N) and hence led to a decrease in its adsorption capacity towards MG dye. High adsorption capacities were found to be 100, 200 and 125 mg/g from MG dye onto AC-S, AC-S/N and AC-S/A, respectively. The adsorption results show that the adsorption was pH dependent with a high adsorption at pH of 6 which is obviously pH of dye solution. The equilibrium adsorption data were analyzed by Langmuir, Freundlich and FlorryHuggins isotherm models. Pseudo-second-order kinetic model and Langmuir isotherm model showed better fit to the adsorption of MG dye onto the prepared carbons. Overall, this study reveals that the obtained carbons from Atropa belladonna are effective adsorbents in removing dyes from wastewater sources. Finally, the results also suggest that oxidation treatment with nitric acid is more efficient than ammonium persulfate to produce high acidic carbon adsorbents.

Sorption of Cu by humic acid from the decomposition of rice straw in the absence and presence of clay minerals

The sorption of Cu on humic acid (HA) from the decomposition of rice straw in the absence (Ck-HA) and presence of montmorillonite (M-HA), kaolinite (K-HA), gibbsite (Gi-HA) and goethite (Go-HA) was investigated at pH 5.0 by using batch studies combined with isothermal titration calorimetry (ITC) and atomic force microscopy (AFM). Characterization by elemental analysis and potentiometric titration showed the composition difference among these five HA. The sorption capacity and rate increased in the order: M-HA < K-HA < Gi-HA < Ck-HA < Go-HA. ITC results revealed that the sorption process was spontaneous and endothermic. The aggregation of HA particles after sorption were observed by AFM images. The influence of pH and positive correlations between the sorption capacity and the content of acidic functional groups of HA indicated that the dissociated acidic functional groups, especially the dissociation of carboxylic groups in HA played an important role in Cu sorption. Sequential desorption of sorbed Cu showed that the surface bonded fraction (97.6–99.0%) was significantly higher than the ion exchanged fraction (1.0–2.4%). Markedly positive entropies (ΔS, 94.4–104.3 J mol−1 K−1) further demonstrated that Cu binding to HA by forming inner-sphere complexes. The findings of this study would promote the understanding on the environmental impact of the decomposition of organic waste from agricultural production.

Advantages and risks of using steel slag in preparing composts from raw organic waste

ABSTRACTIt had been reported that iron and manganese oxides in steel slag enhanced the production of humic acid (HA) from low-molecular-weight compounds, such as phenolic acids, amino acids, and saccharides. In the present study, this function of steel slag was applied to the composting of raw organic wastes (ROWs). The degree of humification of HAs is an important factor in evaluating compost quality. Thus, HAs were extracted from the prepared composts and the humification parameters were determined, in terms of elemental compositions, acidic functional group contents, molecular weights, spectroscopic parameters from UV–vis absorption and 13C NMR spectra. The timing for adding steel slag affected the degree of humification of HAs in the composts. The weight average molecular weight of a HA when slag was added initially (29 kDa) was significantly higher than when slag was added after elevating the temperature of the compost pile (17–18 kDa). These results show that ROWs are decomposed to low-molecular-weight compounds after the pile temperature is elevated and the presence of slag enhances the polycondensation of these compounds to produce HAs with a higher degree of humification. Because the slag used in the present study contained several-tens ng g−1 to several μg g−1 of toxic elements (B, Cu, Cr, and Zn), leaching tests for these elements from the prepared composts were carried out. Levels for leaching boron from composts prepared by adding slag (0.2–0.4 mg L−1) were obviously higher than the corresponding levels without slag (0.05 mg L−1).

NO removal activity and surface characterization of activated carbon with oxidation modification

Non-pitch coal-based activated carbon (NPAC), using a novel non-pitch binder, was used to inexpensively prepare oxidized activated carbon (NPAC-O0) by oxidation modification of oxygen-depleted. Using a fixed bed reactor and BET, FTIR and XPS techniques, this research investigated the denitrification rate, the changes in acidic/basic surface functional groups, and the mechanism of NOx removal. The results demonstrated that in the preparation of catalyst NPAC-O0, oxygen reacted with microcrystalline edges, defect parts and specific chemical functional groups adsorbed on the surface of NPAC to build and ream pores, such that the total pore volume increased by 30.26%. Additionally, the basic functional group content decreased by 36.42%, which was ascribed to a reduction in the pyridine-like and pyrrolic moieties, whereas the acidic functional group content increased by 128.7%, which was a result of the introduction of CO and OCO groups. The removal of NOx by oxidized activated carbon (NPAC-O0) involves both adsorption and catalytic conversion, where the acidic groups absorbed NH3 and the polar/basic functional groups absorbed O2 and NO enhancing the activated carbon activity. The NH3 adsorption is the critical step in the NH3NOO2 reaction. In the mechanism, the increased acidic CO groups promote chemical absorption of NH3 and assist in H-abstraction of NH3 to formation NH2, which then reacts with adsorbed NO2 or NO to generate N2 and H2O in the presence of oxygen. At 30 °C, the denitrification rate of NPAC-O0 remained at 79.46% after a 140 min reaction.