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Organic fouling caused by dissolved organic matter (DOM) is a critical challenge for membrane technologies. In this study, prediction models for the fouling of commercial polyether sulfone (PES) and regenerated cellulose (RC) ultrafiltration membranes by DOM were established based on the hydrophobicity of DOM. The organic fouling behavior of 40 natural water samples collected from Lake Taihu was investigated. The fouling propensity of water samples on ultrafiltration membranes was evaluated using the fouling index (FI). The hydrophobicity of DOM in water samples was quantified by its partition coefficient in an aqueous two-phase system (K

Specific ion effects on the aggregation behavior of a reference aquatic natural organic matter (NOM), Suwannee River NOM (SRNOM), were investigated using kinetic, titration, calorimetric, and surface tension methods. Monovalent cations induced structural compacting of SRNOM, but not its aggregation. Their ability to induce structural compacting follows the order: Cs+ > Rb+ > K+ > Na+ > Li+. Divalent cations except Mg2+ can readily induce SRNOM aggregation. Their critical coagulation concentrations (CCC) follow the order: CCCSr > CCCCa > CCCBa. Electrokinetic, titration, and calorimetric data suggest that monovalent cations have weak interactions with SRNOM, while divalent cations strongly interact with SRNOM. Overall, the cation specificity in aggregation is determined by cation-NOM interactions and their ability to modulate surface tension. Specific ion effects of monovalent cations correlate to their hydration free energy, while that of divalent cations correlate to the ratio of the hydration entropy of cation to the enthalpy change of cation-NOM interactions. The cation specificity is consistent with the extended Derjaguin-Landau-Verwey-Overbeek theory, and the intermolecular interaction energy is dominated by the Lewis acid-base interactions. Our results suggest that specific cations should be targeted to predict or manipulate intermolecular interactions of aquatic NOM in natural and engineered settings.

Silver has been associated with significant environmental challenges. This study aimed to investigate the photo-reduction of silver ions (Ag+) mediated by dissolved black carbon (DBC), a vital dissolved organic matter released from black carbon. Suwannee River humic acid (SRHA) was used as a comparison group. DBC was observed to effectively mediate the photo-reduction of Ag+ to the silver nanoparticles (nAg) under simulated sunlight. The initial rate of formation of nAg mediated by DBC was approximately 3.0–9.5 times higher than that of nAg mediated by SRHA. The Ag+ concentration required to form nAg in the DBC solution was observed to be only 0.5 mg L−1, which was one-tenth of the concentration in the SRHA solution. Further, the mediation efficiency of DBC was higher than that of SRHA, which was attributed to the facilitated ligand-to-metal electron transfer and reduced generation of the oxidative phototransients. The Ag+ sorption played a crucial role during the photo-reduction process by altering the reaction pathway and local Ag+ concentration as well as affecting the initial rate of formation of nAg. Furthermore, the silver seeds generated by DBC are able to trigger the formation of nAg by SRHA at low Ag+ concentrations. Overall, the findings from this study highlight the vital role of DBC in mediating the sunlight-induced speciation of the silver ions.

The fluvial export of dissolved black carbon (DBC) is a major land-ocean flux in the global black carbon cycle, affecting the size of refractory carbon pool in the oceans. The aggregation behavior of DBC is a significant determinant of its transport and vertical mass flux. In this study, the aggregation kinetics and interaction energy of DBC leached from biochar were investigated. DBC was mainly stabilized by hydration force and underwent structural compacting in divalent cation solutions. Na+ and Mg2+ had limited impact on the colloidal stability of DBC due to the strong hydration of these cations. Ca2+ and Ba2+ readily destabilized DBC by forming inner-sphere complexes, reducing its hydrophilicity. Consistently, charge reversal of DBC was observed with high concentrations of Ca2+ and Ba2+. Simulated sunlight exposure led to photo-oxidation of DBC, increasing its colloidal stability. DBC behaved nonconservatively in laboratory mixing experiments using estuary water samples due to aggregation/sedimentatio...

The Three Gorges Dam (TGD) is the largest hydropower facility in the world, influencing the riverine hydrology and mass flux in the Yangtze River. Little is known about its impact on the riverine dissolved organic matter (DOM) quality. In this work, the water quality and DOM quality for water samples collected from the upstream and downstream sites of TGD were investigated. The presence of TGD significantly affects the quantity and quality of DOM but has no pronounced effect on nutrient concentrations. Upstream DOM had higher concentration but lower average molecular weight and aromaticity than the downstream DOM. The biological processes in the dam reservoir contribute significantly to upstream DOM. In the downstream sites, terrestrial DOM input raises the average molecular weight and aromaticity of the overall DOM pool. These results suggest that TGD will influence not only the mass flux of organic carbon but also its quality and lability, which has both environmental and ecological significance.

The intermolecular interactions of natural organic matter (NOM) play a key role in the fate and transport of organic carbon and pollutants in environmental and engineered systems. In this study, the impact of origin and structure on the aggregation behavior of NOM was investigated in the presence of naturally abundant cations. The physicochemical properties of NOM were quantified using a range of indices. Thermodynamic analysis suggests that the colloidal stability of NOM was mainly determined by its hydrophobicity (i.e., Lewis acid-base interactions). All NOM can be coagulated by Ca2+ owing to the strong cation-NOM interactions, which lead to bridging effect and lower Lewis acid-base interactions. Terrestrial NOM can be coagulated by Mg2+ while aquatic NOM cannot, owing to their different hydrophobicity. The critical coagulation concentrations of tested terrestrial NOM in the presence of Ca2+ (CCC–Ca) were quite similar at 1.94–4.88 mM despite their different structural properties. The CCC-Ca of tested aquatic NOM varied significantly from 46.89 mM to 110.40 mM depending on their structure. The optical indices including E2/E3, FI, and HIX can be potentially used as convenient indicators for assessing the colloidal stability of aquatic NOM for water treatment and risk assessment purposes.

Developing low-cost and high-performance catalysts is significant to solar-to-fuel conversion. Here, the synthesis of zero-dimensional (0D) CeO2 nanocrystal-decorated two-dimensional (2D) layered hybrids of MoS2/g-C3N4 was reported for the first time. In the absence of noble-metal cocatalyst, the optimized ternary CeO2@MoS2/g-C3N4 still manifested high photocatalytic activity toward H2 generation, with a rate of 65.4 μmol/h, which is approximately 8.3 and 17.5-fold greater than g-C3N4 and CeO2, respectively. The corresponding apparent external quantum efficiency reached 10.35% at a wavelength of 420 nm. The superior photocatalytic behavior of CeO2@MoS2/g-C3N4 heterojunction could be ascribed to the positive synergetic effects of well-matched energy-level positions and effective charge separation arose from the multi-step electron transfer processes between Ce4+/Ce3+ reversibility pairs and heterostructures. Furthermore, the adsorption ability of reactant H2O molecules on CeO2@MoS2/g-C3N4 was investigated. Due to the interfacial electronic interaction and Ce3+ species, CeO2@MoS2/g-C3N4 presented more reaction active sites with enhanced adsorption capacity and decreased energy barrier for reactant H2O molecules adsorption, which collaboratively promoted photocatalytic water splitting. This study provides new insights into the rational design of inexpensive ternary photocatalyst with multilevel electron transfer for efficiently converting solar energy into hydrogen without noble metals.