Adsorption Of Organic Matter Research Articles

Removal of extracellular free DNA and antibiotic resistance genes from water and wastewater by membranes ranging from microfiltration to reverse osmosis

Free DNA in the effluent from wastewater treatment plants has recently been observed to contain antibiotic resistance genes (ARGs), which may contribute to the spread of antibiotic resistance via horizontal gene transfer in the receiving environment. Technical membrane systems applied in wastewater and drinking water treatment are situated at central nodes between the environmental and human related aspects of the “One Health” approach and are considered as effective barriers for antibiotic resistant bacteria. However, they are not evaluated for their permeability for ARGs encoded in free DNA, which may result, for example, from the release of free DNA after bacterial die-off during particular treatment processes. This study examined the potential and principle mechanisms for the removal of free DNA containing ARGs by technical membrane filtration. Ten different membranes, varied by the charge (neutral and negative) and the molecular weight cut off (in a range from microfiltration to reverse osmosis), were tested for the removal of free DNA (pure supercoiled and linearized plasmids encoding for ARGs and free linear chromosomal DNA with a broader fragment size spectrum) in different water matrices (distilled water and wastewater treatment plant effluent). Our results showed that membranes with a molecular weight cut off smaller than 5000 Da (ultrafiltration, nanofiltration and reverse osmosis) could retain ≥99.80% of free DNA, both pure plasmid and linear fragments of different sizes, whereas microfiltration commonly applied in wastewater treatment showed no retention. Size exclusion was identified as the main retention mechanism. Additionally, surface charging of the membrane and adsorption of free DNA on the membrane surface played a key role in prevention of free DNA permeation. Currently, majority of the applied membranes is negatively charged to prevent adsorption of natural organic matter. In our study, negatively charged membranes showed lower retention of free DNA compared to neutral ones due to repulsion of free DNA molecules, reduced adsorption and decreased blockage of the membrane surface. Therefore, the applied membrane may not be as an effective barrier for ARGs encoded in free DNA, as it would be predicted based only on the molecular weight cut off. Thus, careful considerations of membrane's specifications (molecular weight cut-off and charge) are required during design of a filtration system for retention of free DNA.

Tailored mesoporous biochar sorbents from pinecone biomass for the adsorption of natural organic matter from lake water

Natural organic matter (NOM) raises major issues for drinking water treatment including undesirable taste and color, formation of carcinogenic disinfection by-products, and promotion of microbial regrowth in the water distribution system. As such, mesoporous biochars have been tailored from pine-forestry by-products for treating NOM and color causing compounds from drinking water sources, such as lakes. Herein, several tailored biochars are fabricated via two procedures: pre-pyrolysis/activation/post-pyrolysis and activation/post-pyrolysis processes, using NaOH and ZnCl2 activators to improve the surface chemistry and porous structure for higher NOM adsorption. The mesoporous biochars, pristine biochars, and pinecone biomass are characterized via several analysis methods including Brunauer, Emmett and Teller surface area measurement (BET), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Batch experiments are conducted to study the adsorption isotherm, kinetics and mechanism along with desorption. Characterization revealed effective characteristics of tailored biochars for NOM adsorption including mesoporous structure, remarkable surface area (up to 1470 m2/g), high thermal stability, and elevated carbon content. All the tailored biochars showed improved removal capacities for NOM and color compounds from real lake water samples compared with those of the pinecone biomass and pristine biochars. The most promising tailored biochar (herein named as TB-N-I) was developed by NaOH modification via pre- and post-pyrolysis processes. With the lowest optimized dosage (0.25 g/L), TB-N-I removed >80% of both NOM and color from the lake water (chemical oxygen demand (COD): 13.4 and color: 53.65 mg/L), superior to the removal capacity of commercial powdered activated carbon (PAC). Acidic conditions significantly favored the adsorption, e.g. NOM removal by TB-N-I from the lake water reached 97% at pH 2. Nonlinear regression provided a good fit for Freundlich and Sips (r2 = 0.988 and Δq = 0.08) isotherms as well as pseudo-second-order kinetic models. This suggests the heterogeneous distribution of the adsorptive sites at the biochar surface and the multilayer nature of NOM adsorption. Our desorption study revealed that more alkaline solutions resulted in higher NOM desorption (30 mM NaOH > 3 mM NaOH > distilled water), yielding regenerated adsorbents with high re-adsorption capacity. Liquid chromatograph–organic carbon detection (LC-OCD) was used to study the removal of different size fractions of NOM, e.g. complex humic substances and low molar mass acids. Of significant interest, low molar mass (LMM) fraction, which are more hydrophilic and resistant to conventional treatments, were effectively removed. LC-OCD indicated that TB-N-I removed 20% more of the problematic LMM compared with that of PAC. Effective pore size distribution of tailored biochar (TB-N-I) was indicated by BET analysis and was confirmed by LC-OCD results for the adsorption of NOM fractions.

Reuse of shale gas flowback and produced water: Effects of coagulation and adsorption on ultrafiltration, reverse osmosis combined process

The shale gas flowback and produced water (FPW) from hydraulic fracturing in the Sichuan province of China has relatively low to moderate levels of total dissolved solids (<20 g/L) and organics (<50 mg/L of dissolved organic carbon). As such, a combined ultrafiltration (UF), reverse osmosis (RO) system can be successfully applied to desalinate this feed water with the goal of reuse. However, the concentration of influent organic matter and particulates in the UF and RO stage is high, and the overall ionic and organics composition is highly complex, so that the membrane processes do not perform well, also due to fouling. To ensure the long-term and efficient operation of the UF-RO stages, a combined pretreatment of the FPW with coagulation and adsorption was investigated. The effect of different parameters on the performance on the system was studied in detail. Overall, the coagulation-adsorption pre-treatment greatly reduced fouling of the membrane processes, thanks to the high removal rate of turbidity (98.8%) and dissolved organic carbon (86.3%). The adsorption of organic matter by powdered activated carbon was best described by the Freundlich equilibrium model, with a pseudo second-order model representing the adsorption kinetics. Also, the various ions had competitive removal rates during the adsorption step, a phenomenon reported for the first time for FPW treatment. Also, an optimal dose of activated carbon existed to maximize fouling reduction and effluent quality. The overall treatment system produced a high-quality water streams, suitable for reuse.

Adsorption of organic matter on clay minerals in the Dajiuhu peat soil chronosequence, South China

Clay minerals play important roles in stabilizing organic matter (OM) in soils. In order to investigate the nature of OM in association with clay minerals in peatland soils, the coarse (>0.3 mm) and clay (<2 μm) fractions of samples from a 250-cm-long core from the Dajiuhu peatland in Hubei Province (central China) were analyzed using gas chromatography–mass spectrometry (GC–MS), solid state 13C nuclear magnetic resonance (NMR) spectroscopy, and Fourier transform infrared spectrophotometry (FTIR) methods. The n-alkanes consist mainly of carbon numbers of C21 to C33 and show odd-over-even predominance. Alkanes associated with clay minerals are better protected from biodegradation in old soils, whereas clay minerals in young soils are less favorable for OM interaction. Fatty acids are mainly saturated straight-chain acids (C12–C30), with minor branched and unsaturated acids, showing even-over-odd predominance. The wide distribution of short-chain fatty acids in the soils indicates intensive microbial activity. NMR results confirmed the occurrence of alkyl C, O-alkyl C, aryl C, and carboxyl C in the soil deposits. Aromatic compounds are prone to adsorb to clay minerals, and their abundances in the clay fraction increase as diagenesis proceeds. Polysaccharides are present mainly in young soils and are observed strongly binding to clay minerals, but these compounds are prone to microbial degradation due to their structural instability. Aromatic compounds are bound mainly on the silicon-basal planes. In general, old soils are characterized by stronger chemical interactions between aromatic compounds and clay minerals, as reflected by their lower band positions. Nevertheless, only small amounts of aromatic compounds were found chemically complexed with clay minerals, while most OM in the samples was physically trapped by clay-mineral aggregates. Preservation of OM in the lower profile of the peat soils is mainly attributed to persistently reducing conditions.

Selective adsorption of soil humic acid on binary systems containing kaolinite and goethite: Assessment of sorbent interactions

Inorganic colloids are ubiquitous in soils and coexist as simple mixtures or as strong associations of particles. The coexisting inorganic colloids with a variety of active sites can selectively adsorb humic substances and thus affect the availability and mobility of organic matter. To investigate the selective adsorption of organic matter by coexisting inorganic colloids, humic acid (JGHA) extracted from soil, a kaolinite and goethite synthetic association (KGA) and a kaolinite and goethite mixture (KGM) were prepared and studied. With the adsorption expressed in μmol m−2, the adsorption affinity of JGHA on KGA (initial slope of isotherms) was slightly higher than that on KGM, although KGM could adsorb more JGHA molecules at larger JGHA concentrations. At pH 4, JGHA was adsorbed on the kaolinite edges and goethite through electrostatic attraction and ligand exchange, and on the kaolinite siloxane plates through hydrophobic interaction. At pH 6 and 8, the adsorption occurred only on the kaolinite siloxane plates and goethite. The overall average adsorption Gibbs energies were moderately negative, and comprised a strongly negative average overall molar entropy and a negative average overall molar entropy contribution. Thus, overall JGHA adsorption on KGA and KGM was enthalpy controlled. The large exothermic enthalpy gains and entropy losses were a result of electrostatic attraction and ligand exchange. The entropy gains because of hydrophobic attraction between JGHA and the kaolinite siloxane plates are masked by the larger entropy loss of adsorption on the hydrophilic surfaces. The fractions of JGHA with molar mass &gt;~12.9 kDa (1 Da = 1 g mol−1) were adsorbed selectively by KGM, whereas the fractions &lt;~12.9 kDa were selectively adsorbed by KGA. High molar mass and hydrophobic fractions adsorb selectively on the kaolinite siloxane plates, whereas low molar mass fractions with hydrophilic groups adsorb selectively on goethite and the kaolinite edges.Highlights Selective adsorption behaviour of HA on binary systems containing kaolinite and goethite. High molar mass and hydrophobic HA fractions selectively adsorb on kaolinite siloxane plates. Low molar mass and hydrophilic HA fractions selectively adsorb on kaolinite edges and goethite. Binding affinity of HA to KGA is stronger than to KGM; mineral associations are more beneficial for fixing OM in soil.

In the Search for Nanospecific Effects of Dissolution of Metallic Nanoparticles at Freshwater-Like Conditions: A Critical Review.

Knowledge on relations between particle properties and dissolution/transformation characteristics of metal and metal oxide nanoparticles (NPs) in freshwater is important for risk assessment and product development. This critical review aims to elucidate nanospecific effects on dissolution of metallic NPs in freshwater and similar media. Dissolution rate constants are compiled and analyzed for NPs of silver (Ag), copper (Cu), copper oxide/hydroxide (CuO, Cu(OH)2), zinc oxide (ZnO), manganese (Mn), and aluminum (Al), showing largely varying (orders of magnitude) constants when modeled using first order kinetics. An effect of small primary sizes (<15 nm) was observed, leading to increased dissolution rate constants and solubility in some cases. However, the often extensive particle agglomeration can result in reduced nanospecific effects on dissolution and also an increased uncertainty related to the surface area, a parameter that largely influence the extent of dissolution. Promising ways to model surface areas of NPs in solution using fractal dimensions and size distributions are discussed in addition to nanospecific aspects related to other processes such as corrosion, adsorption of natural organic matter (NOM), presence of capping agents, and existence of surface defects. The importance of the experimental design on the results of dissolution experiments of metal and metal oxide NPs is moreover highlighted, including the influence of ionic metal solubility and choice of particle dispersion methodology.

Study on Effects of External Water Amount on Organic Intercalation of Montmorillonite and Its Mechanism

As an important clay mineral, montmorillonite (MMT) plays a pivotal role in various fields. Water has significant effects on the organification process of MMT, which is associated with the adsorption of organic matter onto MMT with different water contents. In this study, the influence of external water content on the organic intercalation of MMT and its mechanism are discussed from both experimental and simulation results. These results reveal that as the external water content increases, the interlayer spacing of organic MMT increases first and then decreases, while the degree of organification becomes increasingly stronger. Although the interlayer spacing of the organic MMT is the largest when the external water amount is relatively small (e.g., 10%), the molecular arrangement is disorderly and uneven, resulting in a low degree of organification. Increasing the external water content results in a more regular molecular arrangement, more compact intermolecular agglomerates, and a higher degree of order. Therefore, the addition of water plays a crucial role in the organification process of MMT, and the appropriate manufacturing technology should be selected according to the application field. The results of this study provide theoretical support for the preparation of organic MMT and also offer insight into the mechanism of organic intercalation.

Adsorption of organic matter in oil sands process water (OSPW) by carbon xerogel

This study illustrated the preparation, characterization and the use of carbon xerogel materials for the adsorption of acid-extractable fractions (AEF) and naphthenic acids (NAs) from oil sands process water (OSPW). Adsorption results demonstrated that the mesoporous carbonaceous material can successfully be used to adsorb persistent and toxic organic contaminants from OSPW. Carbon xerogel (CX) made at pH 5.5 showed high surface area (573 m2/g) and removed a larger amount of AEF than CX made at pH 6.9 (391 m2/g). The adsorption equilibrium was reached by 24 h for both AEF and classical NAs. 74.6% of AEF and 88.8% of classical NAs were removed by CX5.5 during 24-h adsorption. With respect to classical NAs, a larger the carbon number resulted in higher NA removal. Carbon number had more influence on NA removal when compared with hydrogen deficiency resulting from rings or unsaturated bonding formation (–Z number). The equilibrium adsorption capacity was found to be 15 mg AEF/g and 7.8 mg NAs/g for CX5.5. Adsorption of AEF and classical NAs onto CX5.5 followed pseudo-second order kinetics. With respect to diffusion of AEF and NAs, there were three distinct diffusion regions: bulk, film and pore. Pore diffusion had the lowest rate constant in all cases analyzed and was thus the rate limiting step. The results of this study showed that a mesoporous carbonaceous material such as CX may have the potential to be utilized in a fixed bed adsorption/filtration systems for continuous treatment of OSPW or as a semi-passive treatment method in pit lakes for the removal of organic constituents from OSPW.

Anti-Fouling and Anti-Bacterial Modification of Poly(vinylidene fluoride) Membrane by Blending with the Capsaicin-Based Copolymer.

Membrane fouling induced by the adsorption of organic matter, and adhesion and propagation of bacteria onto the surfaces, is the major obstacle for the wide application of membrane technology. In this work, the capsaicin-based copolymer (PMMA-PACMO-Capsaicin) was synthesized via radical copolymerization using methyl methacrylate (MMA), N-acrylomorpholine (ACMO) and 8-methyl-N-vanillyl-6-nonenamide (capsaicin) as monomers. Subsequently, the capsaicin-based copolymer was readily blended with PVDF to fabricate PVDF/PMMA-PACMO-Capsaicin flat sheet membrane via immersed phase inversion method. The effects of copolymer concentration on the structure and performance of resultant membranes were evaluated systematically. With increase of PMMA-PACMO-Capsaicin copolymer concentration in the casting solution, the sponge-like layer at the membrane cross-section transfers to macroviod, and the pore size and porosity of membranes increase remarkably. The adsorbed bovine serum albumin protein (BSA) amounts to PVDF/PMMA-PACMO-Capsaicin membranes decrease significantly because of the enhanced surface hydrophilicty. During the cycle filtration of pure water and BSA solution, the prepared PVDF/PMMA-PACMO-Capsaicin membranes have a higher flux recovery ratio (FFR) and lower irreversible membrane fouling ratio (Rir), as compared with pristine PVDF membrane. PVDF/PMMA-PACMO-Capsaicin membrane is found to suppress the growth and propagation of Staphylococcus aureus bacteria, achieving an anti-bacterial efficiency of 88.5%. These results confirm that the anti-fouling and anti-bacterial properties of PVDF membrane are enhanced obviously by blending with the PMMA-PACMO-Capsaicin copolymer.

Effects of metal cations on coupled birnessite structural transformation and natural organic matter adsorption and oxidation

Abstract Birnessite, a layered manganese (Mn) oxide, possesses extraordinary metal adsorption and oxidation activity, and thus imposes impacts on many biogeochemical processes. The reactivity of birnessite strongly relies on its Mn oxidation state composition (the proportions of Mn II, III and IV), particularly by the Mn(III) proportion. Partial reduction of birnessite transforms birnessite to be Mn(II, III)-rich or to MnOOH and Mn3O4, and thus strongly affects birnessite reactivity. As a metal scavenger, naturally occurring birnessite contains abundant transition and alkali and alkaline earth metal cations in its structure; however, the effects of these metal cations on the partial reduction-induced transformation of birnessite remain unknown. We examined the effects of Zn2+, Mg2+, Ca2+ and ionic strength (controlled by NaCl) on transformation of birnessite (δ-MnO2) and adsorption and oxidation of natural organic matter during partial reduction by fulvic acid (FA) at pH 8 and FA/MnO2 mass ratios (R) of 0.1 or 1 over 600 h under anoxic conditions. Results showed that low ionic strength (0 versus 50 mM NaCl) disfavored FA adsorption, fractionation and oxidation, and thus disfavored formation of Mn(III) in the reacted birnessite. Compared to the 50 mM NaCl system, all divalent cations (Mg2+, Ca2+ and Zn2+) favored FA adsorption and fractionation. Both Mg2+ and Ca2+ significantly enhanced FA oxidation at the early stage but barely at the late stage, whereas Zn2+ strongly suppressed FA oxidation during the entire experimental period. Due to adsorption competition, the presence of the divalent cations resulted in low concentration of Mn(II) adsorbed on vacancies of birnessite. Both Ca2+ and Mg2+ favored Mn(III) production in MnO6 layers, while Zn2+ inhibited it. A small portion of birnessite also transformed to feitknechtite and hausmannite, and the transformation seemed faster in the presence of Ca2+ or Mg2+ than in NaCl solution. In the presence of Zn2+ at the high FA/MnO2 ratio (R = 1), Zn-substituted hansmannite formed extenstively. The formation of Mn(III) in the reacted birnessite can be ascribed to comproportionation between Mn(IV) and Mn(II) adsorbed on either vacancies or edge sites of birnessite. The low-valence Mn oxide phases likely formed via the comproportionation on the edges. The divalent cations affected Mn(III) concentrations of birnessite and formation of the low-valence Mn oxides by competing with Mn(II) for adsorption on edge/vacancy sites or stabilizing Mn(III) in the layers. This work indicates that divalent metal cations strongly influence reactivity and transformation of birnessite in the coupled Mn and carbon redox cycles, and that birnessite containing divalent cations can be an important adsorbent for natural organic carbon in Mn-rich environments. Overall, this study provides insights into the coupled cycles of Mn, trace metals and organic carbon in alkaline and saline environments.

Kinetic study of humic acid adsorption onto smectite: The role of individual and blend background electrolyte

Many factors can affect the natural organic matter adsorption on clay, such as pH and ionic strength. Blended background electrolyte could be causing better simulation to natural effects. Therefore, kinetic study of humic acid (HA) adsorption onto smectite has been studied under various conditions. Impact of pH and individual and blend background electrolyte with different ionic strength concentration on the rate of adsorption has been investigated. The rate and amount of adsorbed HA on smectite improved with raised background electrolyte concentration, declining pH, and in existence Ca2+. The rate of adsorption order was in the presence of CaCl2 > blend (CaCl2 and KCl) > KCl. The adsorption isotherm was L-shap in the presence of CaCl2 and KCl while was S-shap in presence blend (CaCl2 and KCl). Moreover, the data revealed that the adsorption behavior of HA might be pronounced more obviously by Freundlich model than Langmuir. Two kinetic models were applied to assess the rate constants and kinetic data. The results clarified that HA adsorption on smectite was following to pseudo second order model under various conditions.

Direct Evidence for Temporal Molecular Fractionation of Dissolved Organic Matter at the Iron Oxyhydroxide Interface.

While the importance of organic matter adsorption onto reactive iron-bearing mineral surfaces to carbon stabilization in soils and sediments has been well-established, fundamental understanding of how compounds assemble at the mineral interface remains elusive. Organic matter is thought to layer sequentially onto the mineral surface, forming molecular architecture stratified by bond strength and compound polarity. However, prominent complexation models lack experimental backing, despite the role of such architecture in fractionated, compound-dependent persistence of organic matter and modulating future perturbations in mineral stabilization capacity. Here, we use kinetic assays and ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry under high temporal frequency to directly detect the molecular partitioning of organic matter onto an iron oxyhydroxide during adsorption. We observed three sequential intervals of discrete molecular composition throughout the adsorption reaction, in which rapid primary adsorption of aromatic compounds was followed by secondary lignin-like and tertiary aliphatic compounds. These findings, paired with observed differential fractionation along formulas nitrogen and oxygen content and decreasing selective sorption with reaction time, support "zonal" assembly models. This work presents direct detection of sequential molecular assembly of organic matter at the mineral interface, an important yet abstruse regulator of carbon stabilization and composition across temporal and spatial scales.

Exchanges of nitrogen and phosphorus across the sediment-water interface influenced by the external suspended particulate matter and the residual matter after dredging

Dredging is frequently implemented for the reduction of internal nitrogen (N) and phosphorus (P) loadings and the control of eutrophication. Residuals during dredging activities and external pollution loadings after dredging both commonly contribute to influence the effectiveness of dredging and have been widely discussed. In the current study, the exchanges of N and P across the sediment-water interface (SWI) to these two factors were compared in a six-month field incubation experiment. The results showed that the continuous deposition of external suspended particulate matter (SPM) led ammonium nitrogen (NH4+N) and soluble reactive phosphorus (SRP) fluxes across the newly formed SWI to increase by factors of 4.16 and 12.71, respectively, while residual material caused the same fluxes to increase by factors of 2.06 and 5.06. Both the deposition of external SPM and the residual matter led to higher increase of the fluxes of P across the SWI than those of the fluxes of N across the SWI after dredging. The SPM easily adsorbed P in the water due to extensive adsorption of water soluble organic matter (consisting primarily of easily-decomposed humic-like substances), iron, and aluminum. However, the decomposition of organic matter in the SPM after the deposition on the dredged sediment accelerated the dissolution of redox-sensitive P and organic P across the SWI after dredging. Both the increase in the fluxes of N and P across the SWI would further increase the concentrations of N and P in the overlying water and thereby aggravate the eutrophication status in lakes. More frequent dredging operations might be necessary to reduce the fluxes of N and P from the sediment due to the continuous influence of the external SPM and the residual matter.

Fe(II)-Induced Mineral Transformation of Ferrihydrite–Organic Matter Adsorption and Co-precipitation Complexes in the Absence and Presence of As(III)

The poorly crystalline ferrihydrite (Fh) is often associated with organic matter (OM) and metal(loid)s, such as arsenic (As). The transformation of Fh to more stable and, hence, less reactive phases is catalyzed by the surface reaction with Fe(II). However, little is known regarding the impact of various specific OM types and the co-existence of OM and As on the secondary mineralization of Fh. Accordingly, we explored the extent and the resulting secondary minerals of Fe(II)-induced transformation of [As(III)-adsorbed] OM–Fh adsorption and co-precipitation complexes, which were synthesized using two types of OM: dissolved organic matter (DOM) extracted from the O horizon of an ultisol and polygalacturonic acid (PGA) as a proxy for polysaccharides. Regardless of OM type, increased contents of the co-precipitated or adsorbed OM led to a decrease in Fh transformation in both the absence and presence of As(III). Adsorbed As(III) caused a decrease in Fh conversion for both pure Fh and OM–Fh complexes. We obser...

Kinetic modeling of a heterogeneous Fenton-type oxidative treatment of complex industrial effluent

This work proposes a kinetic model for the reactions involved in the heterogeneous copper-based Fenton-type oxidation of mixed recalcitrant compounds in a real industrial effluent from the alkaline sulfite treatment of wood. This kind of treatment is unusual in this industry due to the complexity of the effluents and the high costs involved in total mineralization of the organic matter. Nevertheless, conversion of recalcitrant to degradable compounds and catalyst recovery can make the difference. The complexity of the effluent and the great number of compounds formed as intermediates, make extremely difficult the identification and quantification of the individual reactions that occur during oxidation. To solve this drawback TOC parameter was used as a representative measurement. To verify the level of TOC degradation produced by the heterogeneous catalysis reaction, experiences of homogeneous catalysis and adsorption were accomplished. The studied temperature range was 45–80 °C. A “two-step” kinetic model was applied to TOC reduction in heterogeneous and homogeneous oxidations, admitting two sequential steps of oxidation: a first fast stage (“seconds stage”) followed by a slow one (“minutes stages”). Kinetic constants were obtained for both processes and activation energies were also determined for the “minutes stage” step (33.17 kJ/mol and 15.13 kJ/mol, respectively). Homogeneous catalysis studies confirm mass transfer limitations in heterogeneous oxidations. Experiences of adsorption of organic matter on CuO/γ-Al2O3 catalyst demonstrated that this phenomenon is exothermic and cannot be neglected. The activation energy of adsorption was determined as 7.32 kJ/mol. Catalysts were characterized through SEM, EDS, XRD, FTIR, and TGA.Graphical

New insight into the adsorption behaviour of effluent organic matter on organic-inorganic ultrafiltration membranes: a combined QCM-D and AFM study.

Adsorption of organic matter on membranes plays a major role in determining the fouling behaviour of membranes. This study investigated effluent organic matter (EfOM) adsorption behaviour onto poly(vinylidene fluoride) (PVDF) membrane blended with SiO2 nanoparticles using quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). The QCM-D results suggested that low adsorption of EfOM and an EfOM layer with a non-rigid and open structure was formed on SiO2-terminated membrane surfaces. Conformational assessment showed that EfOM undergoes adsorption via two steps: (i) in the initial stage, a rapid adsorption of EfOM accumulated onto the membrane; (ii) the change in dissipation was still occurring when the adsorption frequency reached balance, and the layer tended towards a more rearranged or organized secondary structure upon adsorption onto the more hydrophilic surface. For the AFM force test, when a self-made EfOM-coated probe approached the membrane, a ‘jump-in’ was observed for the hydrophobic membrane after repulsion at a small distance, while only repulsive forces were observed for PVDF/SiO2 membranes. This study demonstrated that the PVDF/SiO2 membrane changed the entire filtration process, forming a ‘soft’ open conformation in the foulant layer.

Is the adsorption of soil organic matter to haematite (α‐Fe2O3) temperature dependent?

SummarySoil organic matter interactions with minerals are a key determinant in the long‐term protection and sequestration of carbon in soils and sediments. Climate warming could potentially alter the dynamics of the Earth's largest carbon pools through processes controlling the formation of mineral–organic associations (MOAs). We studied the adsorption of Elliott soil humic acid (HA) and fulvic acid (FA) to the iron oxide mineral haematite (α‐Fe2O3) at temperatures from 15 to 35°C through batch sorption experiments. The ΔG°, ΔH° and ΔS° of sorption were derived for HA and FA and suggested that formation of MOAs was spontaneous and exothermic. The Langmuir sorption coefficients for HA and FA decreased with warming, but the maximum sorption capacities were not temperature dependent. The decrease in sorption coefficient was less when the temperature was increased from 30 to 35°C than from 15 to 30°C. Our infrared, ultraviolet and visible spectroscopy analysis of the bound and unbound HA and FA revealed preferential adsorption of oxygen‐ and hydrogen‐substituted aromatic and aliphatic carbon, which was independent of temperature. The adsorption of a hydrophobic probe molecule, Rose Bengal, to haematite increased with warming. Our results suggest that (i) MOAs in warmer climates might be less sensitive to temperature changes, (ii) the amount of iron oxide‐associated organic matter might remain unchanged with warming and (iii) hydrophobic interactions with iron oxides may be temperature dependent.Highlights How does temperature affect the formation of soil organic matter–iron oxide associations? Warming can change the sorption of organic matter on to minerals thus altering carbon dynamics Warming decreases sorption coefficients, but does not affect maximum sorption capacities The amount of iron oxide-associated organic matter might remain unchanged with warming

Binding of Cd by ferrihydrite organo-mineral composites: Implications for Cd mobility and fate in natural and contaminated environments

Adsorption and coprecipitation of organic matter with iron (hydr)oxides can alter iron (hydr)oxide surface properties and their reactivity towards nutrient elements and heavy metals. Organo−mineral composites were synthesized using humic acid (HA) and iron oxide, during coprecipitation with ferrihydrite (Fh) and adsorption to pre-formed Fh with two C loadings. The Fh−HA coprecipitated composites have a higher C content and smaller surface area compared to the equivalent adsorbed composites. NanoSIMS shows there is a high degree of spatial correlation between Fe and C for both composites, but C distribution is more uniform in the coprecipitated composites. The C 1s NEXAFS reveals a similar C composition between the Fh−HA coprecipitated and adsorbed composites. However composites at high carbon loading are more enriched in aromatic C, likely due to preferential binding of carboxyl functional groups on aromatic rings in the HA. The amount of Cd sorbed is independent of the composite type, either coprecipitated or adsorbed, but is a function of the C loading. Composites with low C loading show Cd sorption that is almost identical to pure Fh, while composites with high C loading show Cd sorption that is intermediate between pure Fh and pure HA, with sorption significantly enhanced over pure Fh at pH < 6.5. A bidentate edge-sharing binding was identified for Cd on pure Fh and Cd-carboxyl binding on pure HA. These findings have significant implications not only for the sequestration of Cd in contaminated environments but also the coupled biogeochemical cycling of Cd, Fe and C in the critical zone.

Assessment of Key Environmental Factors Influencing the Sedimentation and Aggregation Behavior of Zinc Oxide Nanoparticles in Aquatic Environment

Zinc oxide nanoparticles (ZnO NPs) are among the most widely used engineered nanoparticles (ENPs) in various commercial sectors to achieve both social and economic benefits. The post-use release of these NPs to the environment is inevitable, and may pose threat to the human and eco-system. In the present study, we investigated the influence of single and multiple environmental factors on sedimentation behavior of ZnO NPs. The fractional-factorial method based on Taguchi orthogonal array (OA) L27(313) design matrix was used for systematic investigation on the contribution and significance of multiple factors and their interactions. The result of single-factor showed that the ZnO NPs were unstable at or near pHzpc, with high electrolyte concentration; however, the adsorption of natural organic matter (NOM) i.e., humic acid, salicylic acid, and citric acid reverses the surface charge and enhanced NP stability. The Fourier transform infrared (FT-IR) analysis confirms the organic capping ligands on the NP surface. Moreover, the matrix result of analysis of variance (ANOVA) showed that electrolyte concentration and type, and NOM concentration were the most significant factors (p &lt; 0.001) in promoting and influencing aggregation, while the interaction between the factors was also found insignificant. In addition, the result of aggregation kinetics and environmental water samples indicated that the mobility of ENPs may vary substantially in an environment with complex and heterogeneous matrices. This study may contribute to better understanding and prediction of the sedimentation behavior and fate of ZnO NPs in aqueous environments, to facilitate their sustainable use in products and process.

Dwindling vanadium in seawater during the early Cambrian, South China

Elemental vanadium (V), an essentially redox-sensitive metal in seawater, has had a significant impact on the understanding of the evolution of the atmosphere-ocean system throughout the history of the Earth. In fact, the geochemical cycle of V in early Cambrian seawater may have had an influence on the Chengjiang Biota in South China; however, it has not yet been well established. Given the authigenic vanadium accumulation is sensitive to the redox conditions of seawater, here, to constrain the geochemical cycle of V in seawater during the early Cambrian, the Mo, U and total organic carbon (TOC) distributions with high-resolution samples from both the outer shelf and slope facies (e.g., the Duoding and Longbizui sections), are applied to evaluate the redox conditions of ambient seawater. The Mo-U relationships indicate that the redox conditions of the mid-depth seawater evolved in a systematic way in South China, transitioning from an Fe-Mn reduction zone to anoxic/intermittently euxinic states and then to oxic conditions during the early Cambrian. As a consequence, the authigenic V enrichment, constrained by the marine redox conditions, was mainly controlled by the Fe-Mn particulate shuttle and the reduction and adsorption of organic matter in anoxic/euxinic conditions. However, the decoupling among V, Mo, U and TOC under anoxic/euxinic conditions suggests a dwindling vanadium concentration in the early Cambrian seawater of South China. The scavenging efficiency of V from seawater is much higher than those of Mo and U under anoxic/euxinic conditions. Ultimately, these trace elements (e.g., Mo, U, and especially V) in seawater could effectively be regulated and adjusted to a reasonable level under the widespread anoxic/euxinic conditions. The drawdown of trace elements in seawater might provide an early-stage preparation of the marine environment for the subsequent Chengjiang Biota.