Photochemical Synthesis of Selenium Nanospheres of Tunable Size and Colloidal Stability with Simple Diketones.

Temporal and spatial segregations are two fundamental requirements for the successful synthesis of nanoparticles (NPs). To obtain colloidally stable selenium nanospheres (SeNSs), surfactants or polymers are generally needed as structure-directing agents or stabilizers in the reduction approaches for SeNP synthesis. The addition of such chemicals sacrifices the purity of the obtained SeNPs and, therefore, is detrimental to the applications. Here, for the first time, we report that low-molecular weight (less than six carbons) diketones are excellent photoreductants for green and tunable synthesis of SeNPs, owing to their merits in temporal and spatial control. With simple diketones as the photoreductants, the resultant SeNPs were pure and colloidally stable with nice photoelectronic properties. This finding not only provides a useful strategy for the synthesis of SeNPs but also might be a milestone in the development of ketone photochemistry.

An all-in-one approach for synthesis and functionalization of nano colloidal gold with acetylacetone.

Controllable synthesis, proper dispersion, and feasible functionalization are crucial requirements for the application of nanomaterials in many scenarios. Here, we report an all-in-one approach for the synthesis and functionalization of gold nanoparticles (AuNPs) with the simplestß-diketone, acetylacetone (AcAc). With this approach, the particle size of the resultant AuNPs was tunable by simply adjusting the light intensity or AcAc dosage. Moreover, owing to the capping role of AcAc, the resultant AuNPs could be stably dispersed in water for a year without obvious change in morphology and photochemical property. Formation of ligand to metal charge transfer complexes was found to play an important role in the redox conversion of Au with AcAc. Meanwhile, the moderate complexation ability enables the surface AcAc on the AuNPs to undergo ligand exchange reactions (LER). With the aid of Ag+, the AuNPs underwent LER with glutathione and exhibited enhanced photoluminescence (PL) with a maximum of 22-fold increase in PL intensity. The PL response was linear to the concentration of glutathione in the range of 0-500µM. Such a LER makes the obtained AuNPs being good imaging probes. To the best of our knowledge, this is the first work on illustrating the roles of AcAc as a multifunctional ligand in fabrication of NPs, which sheds new light on the surface modulation in synthesis of nanomaterials.

UV-Induced Redox Conversion of Tellurite by Biacetyl.

Tellurium (Te) is a rare element of great value, but it exists mainly in the toxic form of tellurite (TeIV) in water. Effective approaches that are able to reduce the toxicity and recover Te from contaminated water are highly needed. Here, we developed a simple but effective way to reduce toxic TeIV to widely applicable elemental Te0. With the combination of ultraviolet (UV) and biacetyl (BD), the oxidation state of Te could be feasibly changed from IV to 0 or VI. The consumption of dissolved oxygen (DO) was a key factor in the redox conversion of TeIV. Under UV irradiation, BD was first cleaved to acetyl radicals, which could then combine with water molecules to form more reductive diol radicals or combine with DO to form strongly oxidative peroxide radicals. Even without deoxygenation, the UV/BD system could rapidly change from being oxidative to being reductive because of the fast depletion of DO. Owing to the high quantum yield of the acetyl radical, the reduction efficiency of the UV/BD system was about 1 order of magnitude higher than that of UV/sulfite and was more efficient than the commonly used biological methods. This work provides a proof of concept for the reduction of tellurite, which could have relevant implications for water treatment and resource recovery applications.

Antimony (Sb) pollution control by coagulation and membrane filtration in water/wastewater treatment: A comprehensive review.

Antimony (Sb) pollution in the water environment caused by the large-scale mining of Sb ore and the wide use of Sb-containing products seriously endangers human health and poses a great threat to the ecological environment. Coagulation is one of the most cost-effective technologies for Sb pollution control in water/wastewater treatment and has been widely used. However, a comprehensive understanding of Sb pollution control by coagulation, from fundamental research to practical applications, is lacking. In this work, based on the current status of Sb pollution in the water environment, a critical review of the Sb removal performance and mechanism by coagulation and related combined processes was carried out. The influencing factors of Sb removal performance by coagulation are introduced in detail. The internal mechanisms and improvement strategies of Sb removal by oxidation/reduction-coagulation and coagulation-membrane filtration technologies are emphasized. Moreover, given the development of Sb-removing coagulants and the resource utilization of Sb-containing sludge, future perspectives of coagulation for Sb removal are discussed. As the first review in this field, this work will illuminate avenues of basic research and practical applications for Sb and Sb-like pollution control in water/wastewater treatment.

Advantages of Bimetallic Organic Frameworks in the Adsorption, Catalysis and Detection for Water Contaminants.

The binary metal organic framework (MOF) is composed of two heterometallic ions bonded to an organic ligand. Compared with monometallic MOFs, bimetallic MOFs have greatly improved in terms of structure, porosity, active site, adsorption, selectivity, and stability, which has attracted wide attention. At present, many effective strategies have been designed for the synthesis of bimetallic MOF-based nanomaterials with specific morphology, structure, and function. The results show that bimetallic MOF-based nanocomposites could achieve multiple synergistic effects, which will greatly improve their research in the fields of adsorption, catalysis, energy storage, sensing, and so on. In this review, the main preparation methods of bimetallic MOFs-based materials are summarized, with emphasis on their applications in adsorption, catalysis, and detection of target pollutants in water environments, and perspectives on the future development of bimetallic MOFs-based nanomaterials in the field of water are presented.

The suitability of titanium salts in coagulation removal of micropollutants and in alleviation of membrane fouling.

Coagulation is a conventional method in water treatment. In recent decades, with the rapid development of membrane filtration, the use of coagulation is facing some new challenges. How to minimize the membrane fouling became a leading-edge topic in the study of coagulation. Here, the performances of three types of titanium coagulants were evaluated in terms of both the coagulation removal of toxic micropollutants and the alleviation of membrane fouling. Three oxysalts and two antibiotics were taken as representatives of inorganic and organic micropollutants. As compared with titanium tetrachloride (TiCl4) and polytitanium chloride (PTC), titanium xerogel (TXC) with a higher polymerization degree showed much better performances in direct coagulation removal of oxysalts and antibiotics and in pre-coagulation for mitigating membrane fouling in both coagulation-sedimentation-ultrafiltration (CSUF) and in-line coagulation-ultrafiltration (CUF) processes. In the CSUF system, the membrane permeate flux with TXC pre-coagulation (89.5%) was much higher than those of TiCl4 (56.1%) and PTC (57.4%). After a 5 day continuous operation, the transmembrane pressure in the CUF system with TXC coagulation was increased only to 4.9 kPa, while those of PTC and TiCl4 were 12.2 and 18.5 kPa, respectively. The results here demonstrate that TXC is a promising coagulant for pollutant removal and membrane fouling alleviation, due to the following merits: better floc properties, weaker pH-dependence, and higher resistance to coordination with organic pollutants. The observation shed new lights on the fabrication and application of coagulants in a wide variety of scenarios.

[Fabrication of Supported Titanium Xerogel Adsorbent and Performance Evaluation for Arsenite Removal].

Although the adsorption capacity of titanium xerogel(TAX) for arsenite(As(Ⅲ)) is high(254 mg·g-1), the adsorption rate is slow. Therefore, TAX was loaded onto activated carbon, sponge, and resin to fabricate a supported adsorbent, and the arsenite removal performance was evaluated. Except sponge, activated carbon and resin could successfully load TAX. The results showed that resin and activated carbon loaded TAX improved the As(Ⅲ) removal performance, and more significantly by the resin-based materials. Through wet digestion and adsorption kinetics experiments, the amount of titanium loaded was approximately 1.4% and 5% in the activated carbon-based(TAX@AC) and resin-based(TAX@resin) materials, respectively. For the initial concentration of 1.0 mg·L-1 As(Ⅲ) solution, the adsorption rate constant of TAX@D201 was 0.85 mg·(g·min) -1, which was 21 times higher than that of unloaded TAX[0.04 mg·(g·min) -1]. Columns packed with TAX@resin could effectively lower arsenite concentration for up to 560 bed volumes, which is 2.8 times greater than that of the iron-based composites with the same metal mass. Therefore, loading TAX on macroporous resin is an effective strategy and provides an effective approach for the application of TAX in arsenite-containing groundwater.

Sludge reduction and cost saving in removal of Cu(II)-EDTA from electroplating wastewater by introducing a low dose of acetylacetone into the Fe(III)/UV/NaOH process.

Cu(II)-EDTA is highly stable in a wide pH range (3.0∼12.0) and hard to be removed by the conventional precipitation method. Fe(III) displacement/UV photolysis/alkaline precipitation [Fe(III)/UV/NaOH] has been proposed as a promising method for the removal of Cu(II)-EDTA. Nevertheless, a high dose of Fe(III) is needed in this combined process, resulting in the production of a large amount of hazardous sludge. The photochemistry of Fe(III) is known to be ligand-dependent. Fe(III)-oxalate complexes are strongly photoactive. However, the addition of oxalic acid to the Fe(III)/UV/NaOH process was of little help. Acetylacetone (AA) is a good chelating ligand for many metals and has been proved as an efficient photo-activator. By introducing a low dose of AA ([AA]/[Cu] = 1.5) into the Fe(III)/UV/NaOH process, the Fe(III) dosage ([Fe]/[Cu]) was reduced from 10.4 to 3.2. As a result, the chemical cost was reduced from 13.9 to 7.6 kW h/m3. Meanwhile, the energy cost in the UV photolysis was reduced from 1066.5 to 752.4 kW h/m3. Most importantly, the sludge yields were reduced from 8.3 to 2.7 kg/m3 in a simulated wastewater and from 101.8 to 30.8 kg/m3 in a real electroplating wastewater. Such a sludge reduction is of great significance in mitigating the load of landfill.

Coagulation removal of fluoride by zirconium tetrachloride: Performance evaluation and mechanism analysis.

Fluoride (F-) pollution is a worldwide issue. Coagulation with aluminum (Al) salts is an efficient and economical method for the removal of F-. However, due to the strong complexation between Al3+ and F-, the residual F- and Al after coagulation usually exceed the limits. Zirconium (Zr) coagulants have drawn increasing attention due to their excellent flocculation ability for organic matter. In this work, the performance and mechanism of ZrCl4 coagulation for F- removal were investigated with the widely used Al2(SO4)3 as a reference. The optimum pH range is 4.0-6.0 for ZrCl4 and 8.0-10.0 for Al2(SO4)3. ZrCl4 was superior to Al2(SO4)3 for F- removal as the initial F- concentration was less than 30.0 mg L-1. Coexisting substances at environmental concentration levels showed negligible effects on F- removal by ZrCl4. Besides the better F- removal, another advantage of ZrCl4 over Al2(SO4)3 was the much lower residual metal concentration in the pH range of 4.0-11.0. The hydrolysis of Al2(SO4)3 was significantly inhibited due to the formation of Al-F complexes while the hydrolysis of ZrCl4 was not influenced even under strongly acidic conditions. Therefore, F- removal by Al2(SO4)3 was mainly achieved by preliminary complexation between Al3+ and F- and subsequent hydrolysis and polymerization of these complexes, while adsorption onto hydrolysates and ion exchange with surface hydroxyl groups were the main ways of F- removal by ZrCl4. The work here provides a new method for F- removal and may shed light on the application of Zr coagulants for other pollutants.

Advantages of titanium xerogel over titanium tetrachloride and polytitanium tetrachloride in coagulation: A mechanism analysis.

Titanium xerogel coagulant (TXC) worked better than titanium tetrachloride (TC) and polytitanium chloride (PTC) in a wider pH/dose range for the removal of turbidity. However, the underlying mechanisms were not comprehensively understood. In this work, the better coagulation performance of TXC than TC and PTC was systematically elucidated from the following aspects: the physicochemical properties of the three coagulants, the removal of turbidity and organic matter, and the complexation reactions in coagulation. The results demonstrate that the merits of TXC were attributable to the following characteristics: (1) the higher surface charge density/total surface site concentration/isoelectric point of TXC hydrolysates, (2) the formation of TXC hydrolysates with a net-work structure, and (3) the strong binding affinity of TXC hydrolysates to organic matter caused by the bonded acetylacetone in the TXC framework. In short, the hydrolysis behavior of TXC significantly differed from both its precursor, TC, and the prehydrolyzed PTC. The difference in the hydrolysis of TXC was derived from the gelation process, which led to the polymerization of Ti in a way different from prehydrolyzation. The elucidation of the hydrolysis mechanisms is useful for the better application of Ti-based coagulants and may shed light on the preparation of other metal salts.