High Humic Acid Content Research Articles

Protaetia brevitarsis larvae can feed on and convert spent mushroom substrate from Auricularia auricula and Lentinula edodes cultivation

The edible mushroom industry produces massive amounts of spent mushroom substrate (SMS). Thus, there is an urgent need for high-value utilization technology to process the SMS, especially SMSs originating from woodchips. Protaetia brevitarsis larvae (PBL) can feed on various types of organic matter and can produce organic fertilizer and insect protein. In this study, we investigated the potential of PBL to utilize and convert SMSs from Auricularia auricula (SMS-AA) and Lentinula edodes (SMS-LE) cultivation. The results showed that the PBL were able to feed on SMS-AA and SMS-LE and form nutrient-enriched organic fertilizer with a low phytotoxicity and high humic acid content. Further analysis of the organic carbon dynamics suggested that PBL can efficiently digest and utilize lignin. This study demonstrates a new strategy for the utilization of SMSs originating from woodchips, and provides a new model for further investigations on the mechanism of lignin decomposition.

Emerging contaminants removal from effluents with complex matrices by electrooxidation

The electrooxidation of methiocarb and bisphenol A was studied in complex matrices, namely, simulated and real sanitary landfill leachate samples, using a boron-doped diamond anode. With simulated sanitary landfill leachate samples, the influence of the type and ratio of carbon source (glucose/humic acid) and electrolyte (NaCl or Na2SO4) on the emerging contaminants removal was assessed. Using real sanitary landfill leachate, the influence of current density was evaluated. The experimental results showed that electrooxidation, using a boron-doped diamond anode, can be successfully utilized to degrade methiocarb and bisphenol A when present in complex matrices, such as sanitary landfill leachate, and that methiocarb is more easily oxidized than bisphenol A. Furthermore, it was found that the presence of chloride and high humic acid content increases emerging contaminants removal rate, showing that electrooxidation at boron-doped diamond is particularly adequate to solve the problems raised by sanitary landfill leachate, even when contaminated with emerging contaminants.

Cu2+ activated persulfate for sulfamethazine degradation

Sulfonamide antibiotics (SAs) are widely used in veterinary medicine but are poorly metabolized in biological systems; thus, they can cause a selective pressure to promote the proliferation of antibiotic resistant pathogens and threaten human health. Persulfate (PS)-based advanced oxidation processes (AOPs) have been applied for SA degradation, but using transition metal ions as PS activators is relatively limited. In this study, sulfamethazine (SMZ) was used as a model SA to evaluate the performance of a Cu2+ -activated PS system. Cu2+-PS exhibited better SMZ removal than other metal ions, and 25 mg/L SMZ can be degraded in the presence of 0.2 mM Cu2+ and 2.5 g L−1 PS within 120 min. Various anions inhibited SMZ degradation to different degrees except HCO3−. Among the cations, Fe3+ significantly inhibited SMZ removal, while Ni2+ increased the removal rate. High concentrations of humic acid and protein also increased the degradation rate of SMZ. Radical and singlet oxygen quenching experiments, together with the results of electron spin-resonance spectroscopy (ESR), showed that the main active species generated from Cu2+-PS are SO4·- and ·OH. The degradation pathway of SMZ was identified through HPLC-HRMS. Direct SO4·- and ·OH oxidation products of SMZ were not found, suggesting that the complex formed between Cu2+ and SMZ may affect the fate of SMZ. On the other hand, the efficiency and selectivity of Cu2+-PS against different SAs were confirmed. Overall, this study provides a facile and effective method for SMZ and other SA removal.

Study on fluorescence interaction between humic acid and PAHs based on two-dimensional correlation spectroscopy

Polycyclic aromatic hydrocarbons (PAHs) pollution is an increasingly serious environmental problem, and the effective and rapid detection of PAHs is in urgent need for environment management and remediation. At present, fluorescence technology is the preferred method for fast in-situ dynamic detection of PAHs. However, the impact of humic acid on PAHs fluorescence has become a bottleneck for accurate detection of PAHs using this technology. In this work, 2D correlation analysis is used to study the interaction between the fluorescence spectroscopy of humic acid and benzo[ghi]perylene (BGP), a typical molecule in the PAHs family. First of all, the fluorescence characteristics of BGP and humic acid were analyzed and feature peaks were identified separately. Meanwhile, the fluorescence spectra of humic acids at various concentrations excited at different wavelengths were obtained to analyze the variation of fluorescence intensity with concentration for different groups of humic acid. Secondly, the conventional one-dimensional fluorescence spectra of the mixed samples of different concentrations of humic acids with fixed BGP concentration were studied to explore the effect of humic acid on the fluorescence of BGP. Finally, 2D correlation fluorescence spectra of the mixed samples of humic acid and BGP were studied with excitation wavelength as the external perturbation. The results showed that humic acid had a significant effect on the fluorescence intensity of BGP, and indicated that high concentration of humic acid could lead to fluorescence quenching of BGP. And the fluorescence characteristic information of humic acid with lower concentration could be extracted from sliced asynchronous spectrum at the signature peak of BGP. This study demonstrated a novel approach for the separation of fluorescence intensities of humic acid from PAHs, providing corrected PAHs spectra for quantitative analysis of the mixture.

Exploring sorption behaviors of Se(IV) and Se(VI) on Beishan granite: Batch, ATR-FTIR, and XPS investigations

As the important anions in the high-level radioactive waste (HLRW), and the sorption behaviors of Se(VI) and Se(IV) on Beishan granite are important to the safe evaluation and performance assessment of the deep geological repository for HLRW in China. In this study, the sorption behaviors of Se(IV) and Se(VI) on Beishan granite were investigated under different environmental factors combining batch and spectroscopic approaches, such as X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transformed infrared (ATR-FTIR). The results showed that Se(IV) sorption on Beishan granite was much higher than that of Se(VI) mainly due to their molecule charge densities and speciation in solution. The sorption of Se(IV) was independent of ionic strength, suggesting that the inner-sphere complexes (ISCs) was dominant for Se(IV) sorption on granite. However, Se(VI) sorption on Beishan granite was strongly dependent on ionic strength, which indicated that ion exchange and outer-sphere complexes (OSCs) dominated Se(VI) sorption. ATR-FTIR confirmed that Se(IV) and humic acid (HA) could form a soluble complex of HA-Se(IV) in solution. Therefore, under low pH and HA concentration conditions, the presence of HA could enhance Se(IV) sorption; while inhibited Se(IV) sorption on granite to some extent under high pH and HA concentration conditions. In case of Se(VI), the presence of HA greatly reduced the surface charge density of the Beishan granite, which in turn enhanced the electrostatic repulsion of Se(VI) and granite surfaces, thereby inhibiting Se(VI) sorption on granite surface. When Se(IV) coexisted with Eu (III), the sorption of Se(IV) on granite could be enhanced to a large extent, which might be due to the formation of Eu2(SeO3)3 complex with Se(IV) under alkaline condition (consistent with ATR-FTIR), or surface charge modifications of Beishan granite caused by Eu(III) sorption. Owing to the ISCs of Se(IV) on granite, the presence of anions almost no obvious effect on Se(IV) sorption except for SO32− and HPO42− in terms of the competitive sorption, which inhibited Se(IV) sorption to some extent. It was interesting that CO32− could enhance Se(IV) sorption to a large extent, however the mechanism was still not clear. Furthermore, XPS further confirmed that Se(IV) sorption on granite was dominated by Fe(II) and Fe(III), and the host mineral was biotite.

Formation and Transport of Cr(III)-NOM-Fe Colloids upon Reaction of Cr(VI) with NOM-Fe(II) Colloids at Anoxic–Oxic Interfaces

Natural organic matter-iron (NOM-Fe) colloids are ubiquitous at anoxic-oxic interfaces of subsurface environments. Fe(II) or NOM can chemically reduce Cr(VI) to Cr(III), and the formation of Cr(III)-NOM-Fe colloids can control the fate and transport of Cr. We explored the formation and transport of Cr(III)-humic acid (HA)-Fe colloids upon reaction of Cr(VI) with HA-Fe(II) colloids over a range of environmentally relevant conditions. Cr(VI) was completely reduced by HA-Fe(II) complexes under anoxic conditions, and the formation of Cr(III)-HA-Fe colloids depended on HA concentration (or molar C/Fe ratio) and redox conditions. No colloids formed at HA concentrations below 3.5 mg C/L (C/Fe ratio below 1.6), but Cr(III)-HA-Fe colloids formed at higher HA concentrations. In column experiments, Cr(III)-HA-Fe(III) colloids formed under oxic conditions were readily transported through sand-packed porous media. Colloidal stability measurements further suggest that Cr(III)-HA-Fe colloids are highly stable and persist for at least 20 days without substantial change in particle size. This stability is attributed to the enrichment of free HA adsorbed on the Cr(III)-HA-Fe colloid surfaces, intensifying the electrostatic and/or steric repulsion interactions between particles. The new insights provided here are important for evaluating the long-term fate and transport of Cr in organic-rich redox transition zones.

Natural organic matter decreases uptake of W(VI), and reduces W(VI) to W(V), during adsorption to ferrihydrite

Tungsten is both naturally occurring and an anthropogenically released contaminant metal in soils, sediments and water systems that typically exits as the soluble tungstate oxyanions, W(VI)O42−. Tungsten mobility and fate are strongly dependent on the adsorption of tungstate to mineral surfaces. However, environmental mineral surfaces are commonly coated with natural organic matter (NOM), and the role of this coating in the tungsten adsorption process, and thus in controlling tungsten reactivity and transport, is unclear. This study investigates W(VI) adsorption to ferrihydrite (Fh), a ubiquitous iron (hydr)oxide in soils and sediments, both in the absence and presence of humic acid (HA), a widely occurring type of NOM, using batch experiments coupled with spectroscopic and thermodynamic techniques. Kinetic results indicate that access to the adsorption sites for W(VI) on the organomineral surfaces is limited when Fh is coprecipitated with HA. Commensurate with this observation, batch experiments show that HA decreases W(VI) adsorption to Fh over a wide pH range (4–11), and this inhibitory effect is more pronounced at higher HA concentration. X-ray photoelectron spectroscopy (XPS) measurements demonstrate the formation of inner-sphere type W complexes on both the Fh and HA fraction of the Fh-HA binary composite. In particular, ~40% of the adsorbed W(VI) species is reduced to W(V) in the presence of HA. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) results show the presence of poly tungstate species on Fh, particularly at lower pH and in the presence of HA. Isothermal titration calorimetry shows that W(VI) adsorption to Fh is an exothermic process both in the presence and absence of HA, and that process is accompanied by a positive entropy. The findings of this work suggest that NOM not only mobilizes tungstate but also reduces tungstate from W(VI) to W(V) at environmental iron (hydr)oxide-water interfaces, which is of significance for evaluating the migration and bioavailability of tungsten in both natural and contaminated environments.

Enhancement of solar water disinfection using H2O2 generated in situ by electrochemical reduction

In this study, the solar water disinfection (SODIS) process was enhanced by in situ generated H2O2, and the influences of current, temperature, bacterial load, humic acid (HA), and bicarbonate were investigated. The results revealed that 1.29 kJ/L of electricity consumption reduced the treatment time by 40 % and decreased the required solar energy from 235.95–141.58 kJ/L. 1O2 was the main reactive oxygen species (ROS), which played an important role. Increasing the current from 15 to 25 mA improved the cumulative H2O2 production, but it had no effect on the disinfection rate. Bicarbonate markedly suppressed E. coli inactivation. Decreasing the initial E. coli concentration reduced the required treatment time from 180 to 120 min. Increasing the temperature had a positive effect on the disinfection. HA concentration of 1 mg/L was the best for E. coli inactivation. In the presence of higher HA concentrations, it required a longer treatment time.

Boosting the activity and environmental stability of nanoscale zero-valent iron by montmorillonite supporting and sulfidation treatment

Given its high activity and nontoxicity, nanoscale zero-valent iron (nZVI) has been intensively used to remediate the groundwater contaminated by trichloroethylene (TCE). However, the long-term stability of nZVI could be impaired by aging and natural organic matter. Herein, a montmorillonite-supported sulfurated nZVI (S-nZVI/MMT) was successfully synthesized, which exhibited robust activity and stability under environmental conditions through the interlayer interaction of MMT. The removal efficiency of TCE by S-nZVI/MMT reached 78.7%, which was much higher than that by S-nZVI and nZVI/MMT, within 12 h with Fe/S dosage ratio of 1:1 and particle dosage of 4 g/L. Importantly, the presence of high concentration of humic acid (up to 50 mg/L) caused unobvious effect on the performance of S-nZVI/MMT toward TCE removal, and more than 68.1% of removal efficiency of TCE could be maintained when the particle was aged in water for 30 days. The high activity and stability of S-nZVI/MMT may be attributed to the formation of nano-sized S-nZVI clusters in the MMT interlayer, protecting the active sites from passivation of humic acid. This work may promote the application of nZVI under complex natural conditions.

Briquette organo-mineral fertilizer based on humic acids

The results of research on the creation and use of briquette fertilizers with a high content of humic acids, substances of natural origin, which are naturally compatible multifunctional polyampholites, are presented. In briquette fertilizers, the microbiological binder “Biogum” is used as a binder, which is an organo-mineral fertilizer containing various components. Two variants of briquette fertilizers have been developed: tableted and rod fertilizers, which are necessary for successful cultivation of plants, shrubs, and trees.

Explorando el potencial de lodos urbanos para la producción de humus líquido

Worldwide, scientists have long been researching municipal sewage sludge management options in the context of the circular economy. In Chile, in particular, there have been a lot of misgivings about the disposal of sewage sludge. Liquid humus is a solution of humic and fulvic acids that can be used to add organic matter to soil via irrigation. The objective of this study was to evaluate the industrial potential of sewage sludge as a source material for the production of liquid humus. The sludges analyzed in the study produced liquid humus with high concentrations of humic and fulvic acids (7.3–7.9 g L-1). In one sludge under study, humic acids constituted the principal ingredient, while in another sludge, humic and fulvic acids were found in similar proportions. Since the results point to the occurrence of sewage sludge humification, such sludge from wastewater treatment plants may potentially be used as a source for the production of liquid humus. However, future studies are needed to evaluate agronomical performance of liquid humus sourced from urban sewage sludge.

Land–Use Changes Influencing C Sequestration and Quality in Topsoil and Subsoil

Soil capacity as a major carbon (C) sink is influenced by land use. Estimates of soil organic carbon (SOC) sequestration have mostly focused on topsoils [0–30 cm official Intergovernmental Panel on Climate Change (IPCC) soil depth]. We investigated SOC stocks and their quality as influenced by land-use changes. Soil samples were collected from five soil depths down to 100 cm of three adjacent fields each representing a different land use—forest, cassava, and rice paddy—in Northeast Thailand. Sequestration of SOC in topsoils under all land uses was higher, as indicated by SOC stocks (59.0–82.0 Mg ha−1) than subsoils (30–100 cm) (27.0–33.0 Mg ha−1). The soil profile (0–100 cm) of the forest had higher stocks of SOC and humic acid (115.0 and 6.8 Mg ha−1, respectively) than those of cultivated land uses [paddy (100.0 and 4.8 Mg ha−1, respectively) and cassava (87.0 and 2.3 Mg ha−1, respectively)], which accounted for an average 30% increase in SOC sequestration over those with only topsoil. Topsoils of the forest had higher humic acid content but narrower E4:E6 ratio [the ratio of absorbances at 465 nm (E4) and at 665 nm (E6)] of humic acids (2.8), indicating a higher degree of humification and stabilization than the cultivated soils (3.2–3.6). Subsoil C was higher quality, as indicated by the lower E4:E6 ratio of humic acids than topsoils in all land uses.

Effect of leonardite application on leaf nutrient content and fruit chemical parameters of cherry (Prunus avium L.)

Organic fertilizers have an important role in plant nutrition practices by protecting the environment, human health, ecological balance and supporting sustainable productivity. Hence, the use of leonardite which has high humic acid content is becoming increasingly common. Objectives of the study were to examine the effects of leonardite application on leaf nutrient contents and some fruit chemical parameters (pH, total soluble solids, total phenolic content and antioxidant activity) of cherry (Prunus avium L.). Cherry Ziraat 900 was used as a test plant and grafted on a Gisela 6 rootstock. The research was carried out in a randomized block design with three replications and 12 parcels. The 10-year-old orchard was chosen as the research area with having planting space of 5.0 m × 2.5 m. Each parcel consists of 25 trees. Four different doses (0-2-4-8 kg tree−1) were applied to drip lines of trees at a depth of 20 cm. Chemical fertilizers (N-P-K) were also added. The effect of the applications in the research has a statistically significant effect on all parameters analyzed in leaves and fruits except for Mg in leaves. In addition, as the dose of leonardite is increased, its effect was also increased and the results appeared in different groups due to the increase of ionization, mobility and adsorption of chemical fertilizers applied in the research. Nutrient absorption was increased because of the increased permeability of stem cell membrane by leonardite applications. Consequently, nutrient levels in the leaves were sufficient and/or excessive and fruit contents were found optimum.

Degradation of ibuprofen in soil systems by persulfate activated with pyrophosphate chelated Fe(II)

The removal of ibuprofen (IBP) by persulfate (PS) activated with pyrophosphate (SP) chelated Fe(II) was investigated. Results showed that the chelation of SP with Fe(II) can significantly trigger PS to improve IBP degradation in soil systems. Response surface methodology was applied to optimize the dosage of Fe(II)-SP and PS. The optimal dosage was Fe(II)-SP: PS = 1:10 to achieve an IBP degradation efficiency of 72.1% at an initial IBP concentration of 48.4 μM kg−1. The effect of humic acid (HA) on IBP removal was also studied. A low HA concentration accelerated IBP removal efficiency, whereas a high HA concentration suppressed IBP oxidation. pH significantly impacted IBP treatment, and maximum removal was obtained at pH 5.45. The quenching test indicated that HO and SO4− coexisted in soil systems, although SO4− predominated. The steady-state concentrations of SO4− and HO were calculated. The effects of inorganic anions showed that Cl− was concentration-dependent and HCO3− negatively influenced IBP removal from soil. A single PS addition improved the degradation efficiency of IBP, whereas a sequential injection of Fe(II)-SP was conducive to IBP oxidation. Fe(II) exhibited efficient ability to activate PS at an early stage, whereas the separate coupling of PS with seven other metal ions was less efficient. IBP transformation by-products were identified, and a reasonable oxidation pathway was schemed in accordance with gas chromatography-mass spectrometry (GC–MS) results. Soil properties were not severely impacted, and scanning electron microscopy (SEM) showed that HA was more easily oxidized than humin in soil systems.

Co-transport of U(VI), humic acid and colloidal gibbsite in water-saturated porous media

The release of uranyl from uranium tailing sites is a widely concerned environmental issue, with limited investigations on the effect of coexistence of various colloids. Gibbsite colloids extensively exist, together with ubiquitous humic substances, in uranium polluted waters at tailing sites, due to high concentration of dissolved Al in acid mine drainage. In this context, we investigated the co-transport of U(VI), gibbsite colloids and humic acid (HA) as a function of pH and ionic strength at a U(VI) concentration (5.0 × 10−5 M) relevant within mine tailings and related waste. It was found that, owing to electrostatic attraction, gibbsite colloids and HA associated with each other and transported simultaneously regardless of U(VI) presence. Besides the impact of pH and ionic strength, whether gibbsite colloids facilitated U(VI) transport depended on HA concentration. Gibbsite colloids impeded U(VI) transport at relatively low HA concentration (≤5 mg L−1), because associated colloids loaded with U(VI) were positively charged which favored colloid retention on negatively charged quartz sand in the column. U(VI) together with gibbsite colloids and low concentration HA was completely blocked at natural pH and/or high ionic strength. At relatively high HA concentration (20 mg L−1), however, the associated colloids showed negative zeta potential which facilitated U(VI) transport because of repulsion between negatively charged colloids and quartz sand. Meanwhile, high concentration of HA dramatically accelerated the transport of gibbsite colloids. These results implied that gibbsite colloids might imped U(VI) migration at uranium tailing sites unless the aquifers are enriched with abundant humic substances.

Effect of humic acid on Se and Fe transformations in soil during waterlogged incubation

Humic acid (HA) serves as electron donor and acceptor in the biogeochemical cycle of Fe and Se in soil. In anoxic condition, a series of redox reactions occur, including reductive dissolution of Fe oxides, decomposition of organic matters, and transformation of trace elements. Thus, this study demonstrates the effect of HA on Se and Fe transformations in soil during waterlogged incubation. Soils were incubated under anoxic condition for 56 days, and pH, redox potential (Eh), and Fe and Se concentrations were measured at specific reaction times (days 2, 4, 8, 15, 28, and 56 of incubation). Moreover, sequential extraction and X-ray photoelectron spectroscopy (XPS) were used to obtain Se and Fe transformations, respectively. High resolution transmission electron microscopy (HR-TEM) was used to observe the morphology properties of soil. Results indicated that 4% HA addition decreased the pH and inhibited Eh decline continuously, and HA addition inhibited the Fe and Se release from soil. The Se concentration in soil solution without and with 4% HA addition at the day 15 of incubation were 1.05 mg L−1 and 0.30 mg L−1, respectively. Moreover, the residual Se fraction in soil with HA addition was evidently more than that in soil without HA addition. XPS of Se3d and Fe2p revealed that the binding energy of the main peak shifted to low values and the peak shape varied with the increase in HA addition. XPS2p3/2 and HR-TEM data indicated that the surface structure of Fe oxides in soil varied with the variations in anoxic incubation time and HA addition amount. HA addition would negatively influence Se and Fe release in soil solution and then reduce their bioavailability. This study aids in understanding the environmental behavior changes of Se and Fe when high HA concentrations enter the soils, especially wetland or paddy soil.

Coagulation and Dissolution of CuO Nanoparticles in the Presence of Dissolved Organic Matter Under Different pH Values

The increased use of copper oxide nanoparticles (CuO NPs) in commercial products and industrial applications raises concerns about their adverse effects on aquatic life and human health. Therefore, the current study explored the removal of CuO NPs from water via coagulation by measuring solubility under various pH values and humic acid (HA) concentrations. The results showed that the media pH significantly affected the coagulation efficiency of CuO NPs (30 mg/L) under various (0–0.30 mM) ferric chloride (FC) dosages. The concentration of dissolved Cu2+ ions at pH 3–6 was (16.5–4.8 mg/L), which was higher than at other studied pH (7–11). Moreover, the simultaneous effect of coagulants and charge neutralization at pH 6–8 enhanced the removal of CuO NPs. At a lower FC (0–0.05 mM) dosage, the higher HA concentration inhibited the aggregation of CuO NPs. However, at the optimum dose of (0.2 mM) FC, the efficiency of turbidity removal and solubility of CuO NPs between pH 8 and 11 was above 98% and 5%, respectively, probably due to coagulant enmeshment. Our study suggested that coagulation was effective in removing the CuO NPs from the complex matrices with pH values ranging from 8–11. The findings of the present study provide insight into the coagulation and dissolution behavior of CuO NPs during the water treatment process.

Efficient Removal of Lead from Water Using Stabilized Iron Sulfide Nanoparticles: Effectiveness and Effects of Stabilizer

Fully stabilized FeS nanoparticles were prepared with water-soluble carboxymethyl cellulose (CMC) as a stabilizer, and investigated for adsorption of lead (Pb2+) ions from simulated drinking water. The optimum particle stabilization was achieved using 0.0025 wt.% of CMC for 50 mg/L FeS (i.e., CMC-to-FeS molar ratio of 0.0005). The particle stabilization technique increased lead removal from 78.1% to 90.3%. However, further increasing the CMC-to-FeS molar ratio to 0.0025 diminished the removal. Rapid adsorption kinetics of Pb by CMC-FeS was observed with an equilibrium time of 240 min. The kinetic data was adequately fitted by a pseudo-second-order kinetic model. The adsorption isotherm showed a sigmoidal S-shape due to complexation of Pb with soluble CMC molecules, and the Sigmoidal isotherm model well fitted the adsorption isotherm data with a maximum monolayer adsorption capacity of 77.0 mg/g. FTIR and XRD analyses indicated that both surface complexation and chemical precipitation (in the form of PbS) were the dominant adsorption mechanisms. Pb uptake was enhanced with increasing CMC-FeS dosage from 10 to 125 mg/L and increasing pH from 4.5 to 8.5. The material can perform well under typical concentrations of a model humic acid (HA) and salts. Yet, unusually high concentrations of HA or hardness ions may exerted elevated inhibitive effect. The findings indicated that CMC-stabilized FeS nanoparticles are promising for effective immobilization of lead in contaminated water and soil.

Concentration dependent effect of humic acid on the transformations of silver nanoparticles

Influence of humic acid (HA) concentration on the colloidal stability and dissolution of silver nanoparticles (AgNPs) was evaluated in a series of long-term experiments. The stability of freshly synthesized and uncoated AgNPs was investigated as a function of HA concentration (0–250 mg/L). In the absence of HA, AgNPs underwent oxidative dissolution and aggregation disturbing the colloidal stability of AgNPs. In the HA concentration range of 1–20 mg/L, HA stabilized AgNPs due to the inhibition of the release of ionic Ag ensuring the persistence of AgNPs in the aquatic environment for a longer period. At higher concentrations of HA (20–250 mg/L) in the soil environment, AgNPs were wrapped by the HA molecules, increasing the hydrodynamic diameter of the AgNPs. Due to the suppression of dissolution of AgNPs, primary particles remained stable in the environment for a prolonged period with no change in the primary particle size and morphology. Furthermore, it was observed that ionic Ag in the solution can be reduced to form fresh, secondary AgNPs at the lower levels of HA in the aquatic environment, in the presence of sunlight. This study is important in understanding the role of HA on the stability of AgNPs in the natural environment.

Efficient degradation of carbamazepine by organo-montmorillonite supported nCoFe2O4-activated peroxymonosulfate process

Carbamazepine (CBZ) is one of most frequently detected pharmaceutical contaminants in water ecosystem, which cannot be removed efficiently by traditional techniques. Degradation of CBZ by peroxymonosulfate (PMS) activated with organo-montmorillonite supported nCoFe2O4 (nCoFe2O4/OMt) was investigated in this study. The degradation efficiency of CBZ (5 mg L−1) was 93% within 60 min in the presence of 0.4 g L−1 nCoFe2O4/OMt and 0.5 mM PMS at pH 6.8 and 25 °C, following a pseudo-first order kinetics. High PMS concentration and low initial pH could enhance CBZ degradation. The presence of Cl−, NO3− and HCO3− showed marked enhancement, slight suppression and obvious inhibition of CBZ degradation, respectively. High concentration of humic acid could decrease the CBZ degradation. X-ray photoelectron spectroscopy of nCoFe2O4/OMt before and after reaction revealed that both Co2+/Co3+ and Fe2+/Fe3+ were involved in PMS activation during the CBZ degradation. Electron paramagnetic resonance and radical scavenger experiments confirmed that both OH and SO4− played a predominant role on the CBZ degradation. The degradation products were identified by LC–MS/MS to understand the possible pathways.