Effect of iron substitution in cryptomelane on the heterogeneous reaction with isoprene.

Biogenic isoprene is an important pollutant for regional air quality. Being ubiquitously distributed on the earth surface, manganese (hydr)oxides should play a vital role in the transformation of isoprene. Cryptomelane is a typical manganese oxide with isomorphous substitution of Fe for Mn, but less attention has been paid to its heterogeneous reaction with isoprene. When Fe3+ replaces Mn3+, K+ is depleted and Mn3+ is oxidized to Mn4+. In contrast, oxygen vacancies are formed when Fe3+ substitutes Mn4+. Fe substitution creates weak crystallites and abundant mesopores, resulting in the increase of isoprene adsorption. As found by theoretical calculations, the Mn4+-O2- bonds at the cross sections of the tunnels is more active than that on the outer wall of the tunnels. After the adsorption of isoprene, bridging carboxylate species and hydrogen-bonding water are produced and the surface octahedra are distorted, i.e., Mn4+O6 → Mn3+O6-δ. As the heat facilitates the breakage of Mn4+-O2-, the increase of environmental temperature enhances the oxidation of isoprene. The above findings shed light on the effect of Fe substitution in cryptomelane to enhance the oxidation of isoprene, and illustrates that heterogeneous reaction with isoprene impairs the transformation of other environmental substances on cryptomelane.

Harvesting of Microcystis flos-aquae using dissolved air flotation: The inhibitory effect of carboxyl groups in uronic acid-containing carbohydrates.

Harvesting algal biomass reduces nutrient loading in eutrophicated lakes and the protein-rich microalgal biomass could be recycled as feedstocks of feed and fertilizer. Due to the complexity of algogenic organic matter (AOM), the key components and functional groups in AOM that inhibit coagulation-based microalgal harvesting have not been disclosed thus far. This study quantitatively analysed the responsive compositions and functional groups of AOM involved in the dissolved air flotation (DAF) harvesting of M. flos-aquae with 1 × 109 cell L-1 density at coagulation pH 6.2. The results showed that harvesting efficiency dropped drastically from 95.5 ± 0.7% to 43 ± 0.7% in the presence of AOM (26.77 mg L-1) at the coagulant dosage of 0.75 mg L-1 and further deteriorated with increasing AOM concentration. Carbohydrates contributed 81% of the total composition of substances involved in the DAF, while the contribution of protein and humic-like substances were only 18% and 1%, respectively. Stoichiometric analysis of functional groups in carbohydrates, proteins, and humic-like substances using model components revealed that carboxyl groups in uronic acid-containing carbohydrates accounted for 76% of the total reduction in carboxyl groups, which was much higher than that in proteins (23%) and humic-like substances (1%), indicating that carboxyl groups in uronic acids containing carbohydrates were the major inhibitors. A conceptual model of charge competition was proposed to explain the inhibition mechanism of carboxyl functional groups in uronic acid-containing carbohydrates on microalgal DAF. Strategies such as preventing carboxyl deprotonation by pH reduction and employment of sweeping/bridging polymeric coagulants/flocculants were proposed for the to reduce the inhibitory effect of carboxyl functional groups.

Synergistic solidification/stabilization of electrolytic manganese residue and carbide slag.

Electrolytic manganese residue (EMR) contains high concentrations of NH4+ and heavy metals, such as Mn2+, Zn2+, Cu2+, Pb2+, Ni2+ and Co2+, while carbide slag (CS) contains high amount of OH- and CO32-, both posing a serious threat to the ecosystem. In this study, EMR and CS synergistic stabilization/solidification (S/S) was discussed science CS could stabilize or solidify EMR and simultaneously reduce its corrosive. The results showed that after the synergistic S/S for 24 h when liquid-solid ratio was 17.5% and CS dosage was 7%, Mn2+ and NH4+ leaching concentrations of the S/S EMR were below the detection limits (0.02 mg/L and 0.10 mg/L) with a pH value of 8.8, meeting the requirements of the Chinese integrated wastewater discharge standard (GB 8978-1996). Mn2+ was stabilized as MnFe2O4, Mn2SiO4, CaMnSi2O6, and NH4+ escaped as NH3. Zn2+, Cu2+, Pb2+, Ni2+ and Co2+ in EMR can also be stabilized/solidified because of the react with OH- and CO32- in CS. Chemical cost was only $ 0.54 for per ton of EMR synergistic harmless treatment with CS. This study provided a new idea for EMR cost-effective and environment-friendly harmless treatment.

Bifunctional nanozyme of copper organophyllosilicate for the ultrasensitive detection of hydroquinone.

The rapid development of nanozymes for ultrasensitive detection of contaminate has resulted in considerable attention. Herein, a carboxyl- and aminopropyl-functionalized copper organophyllosilicate (Cu-CAP) was synthesized by a facile, one-pot sol-gel method. The bifunctional groups endow it with superior catalytic activity than that of natural enzyme. Besides, it possesses outstanding catalytic stability under harsh conditions such as high temperature, extremely high or low pH, and high salinity. Apart from laccase-mimetic activity, Cu-CAP also shows oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) to the blue-colored TMBox in the presence of H2O2, which is similar to natural horseradish peroxidase (HRP). Interestingly, this colorimetric system was suppressed by hydroquinone (HQ) specifically. Inspired by this, Cu-CAP was used to develop a highly sensitive and selective colorimetric method for the determination of HQ. This assay displayed an extremely low detection limit of 23 nM and was applied for the detection of HQ in environmental water with high accuracy. This approach offers a new route for the rational design of high performance nanozymes for environmental and biosensing applications.

Study on the cell-collector-bubble interfacial interactions during microalgae harvesting using foam flotation.

Foam flotation is an economical and efficient technology for microalgae harvesting. However, the mechanism of cell-collector-bubble interfacial interactions remains to be elucidated. There are two distinct hypotheses regarding the mechanism of microalgae foam flotation. In this study, the cationic surfactant N-cetyl-N-N-N-trimethylammonium bromide (CTAB), which acts as a partition between Chlorella sorokiniana cells and bubbles, is quantified and the zeta potential response of cells and bubbles after adsorption of CTAB is calculated to reveal the interfacial mechanism of the cells-collector-bubble interfacial interactions. The results indicated that more than 90% of CTAB was preferentially adsorbed on the bubbles, which reversed the surface charge of bubbles from negative (-20 mV) to positive (6.1 mV). However, only 0%-3% CTAB was observed on the microalgae cells, suggesting its limited influence on the negatively charged microalgae cells (from -22.3 to -18.6 mV). During microalgae foam flotation, the nonpolar tails of CTAB were first inserted into the bubble through hydrophobic interactions, leaving the positively charged polar heads outside; further, the CTAB-covered positively charged bubbles captured the negatively charged cells by electrostatic attraction. A feasible mechanism was proposed to understand the interfacial interaction of the microalgae cell-CTAB-bubble. By understanding the mechanism of foam flotation, efficient and cost-effective collectors and devices for microalgae harvesting using foam flotation can be developed.

A critical review on approaches for electrolytic manganese residue treatment and disposal technology: Reduction, pretreatment, and reuse.

Electrolytic manganese residue (EMR) has become a barrier to the sustainable development of the electrolytic metallic manganese (EMM) industry. EMR has a great potential to harm local ecosystems and human health, due to it contains high concentrations of soluble pollutant, especially NH4+ and Mn2+, and also the possible dam break risk because of its huge storage. There seems to be not a mature and stable industrial solution for EMR, though a lot of researches have been done in this area. Hence, by fully considering the EMM ecosystem, we analyzed the characteristics and eco-environmental impact of EMR, highlighted state-of-the-art technologies for EMR reduction, pretreatment, and reuse; indicated the factors that block EMR treatment and disposal; and proposed plausible and feasible suggestions to solve this problem. We hope that the results of this review could help solve the problem of EMR and thus promote the sustainable development of EMM industry.

Selective Loading and Prolonged Release of 5-Fluorouracil in the Nanoconfined Interlayer Space of Montmorillonite.

Montmorillonite was used as a carrier for the anticancer drug 5-fluorouracil (5FU). The selective loading of 5FU into the nanoconfined interlayer space of montmorillonite was achieved by rinsing off the weakly bonded 5FU from the external surface. The 5FU loading content in montmorillonite was 3.2 mass%. The intercalated 5FU was in an amorphous state and might be arranged as a roughly vertical monolayer in the interlayer space of montmorillonite. The intercalated 5FU showed a high thermal stability due to the protection of the montmorillonite layers. The release profiles of the intercalated 5FU were well fitted with the modified Korsmeyer-Peppas model. The montmorillonite exhibited a prolonged release of 5FU due to the restriction of the outward diffusion of intercalated 5FU. The 5FU/montmorillonite system has promising potential for oral administration for colonspecific delivery.

Cascade cycling of nicotinamide cofactor in a dual enzyme microsystem.

Encapsulation of two enzymes, alcohol dehydrogenase (ADH) and glucose oxidase (GOx), within peroxidase-like tourmaline microparticle (TM)-based colloidosomes was used to construct a functionalized microsystem capable of sustainable cascade cycling of nicotinamide cofactor (NAD+/NADH) via chemical signaling between spatially confined dual-enzyme and active membranes.

Activation of natural halloysite nanotubes by introducing lanthanum oxycarbonate nanoparticles via co-calcination for outstanding phosphate removal.

Halloysite nanotubes were activated via co-calcination of halloysite and the precursors of lanthanum oxycarbonate (LO), generating reactive alumina nanoparticles and uniformly anchoring LO nanoparticles to halloysite surfaces. The resulting LO-alumina combination exhibits record-high phosphate adsorption capacity as well as excellence in adsorption selectivity and sewage phosphate removal.

Activating 2D nano-kaolinite using hybrid nanoparticles for enhanced phosphate capture.

A synergistic host-guest coupling is exploited to disorder nano-kaolinite unit layers to form Al2O3 nanoparticles, which act as activated adsorptive sites; meanwhile, the coupling enables La-based nanoparticles to anchor homogenously on the nano-kaolinite surfaces, fully utilizing their adsorption ability. The activated hybrid nanostructures exhibit an excellent phosphate adsorption capacity.

A synergetic biomineralization strategy for immobilizing strontium during calcification of the coccolithophore Emiliania huxleyi.

The coccolithophore species Emiliania huxleyi has one of the most global distributions in the modern oceans. They are characteristically covered with calcite scales called coccoliths. In this study, stable strontium immobilization during the calcification process was investigated to indirectly assess a proposed bioremediation approach for removing Sr2+ contamination from marine environments. Results indicate that E. huxleyi has high Sr2+ tolerance and removal efficiency in response to Sr2+ stress ranging from 5.6 to 105.6 ppm. Sr2+ immobilization during E. huxleyi calcification indicates a concentration-dependent synergistic mechanism. At lower concentrations of Sr2+ (25.6 ppm), Sr2+ is incorporated into coccoliths through competitive supply between Sr2+ and Ca2+. In addition, calcite productivity decreases with increased Sr2+ removal efficiency due to crystallographic transformation of coccoliths from hydrated calcite into aragonite at 55.6 ppm Sr2+. Further formation of strontianite at 105.6 ppm Sr2+ is due to precipitation of Sr2+ on the edge of the rims and radial arrays of the coccoliths. Our study implies that coccolithophores are capable of significant removal of Sr2+ from the marine environment.

The interface interaction behavior between E. coli and two kinds of fibrous minerals.

In the present, studies of interaction between human normal flora and fibrous mineral are still lacking. Batch experiments were performed to deal with the interaction of Escherichia coli and two fibrous minerals (brucite and palygorskite), and the interface and liquid phase characteristics in the short-term interaction processes were discussed. The bacterial concentrations, the remnant glucose (GLU), pyruvic acid, and the activity of ß-galactosidase and six elements were measured, and the results show that the promoting effect of brucite on the growth of E. coli was more significant than that of palygorskite. FTIR and XRD analysis results also confirmed E. coli has obviously dissolved on brucite and damage effect on palygorskite silicon structure. SEM results show that the interfacial contact degree between E. coli cells and brucite fibers was higher than that of palygorskite. These may be due to the zeta potential difference between E. coli and palygorskite was 14.57-22.37 mV, while it of brucite was 44.04-64.24 mV. The elements dissolving of two fibrous minerals not only increased regularly to liquid EC but also had a good buffer effect to the decrease of liquid pH. Studies of short-term interaction between E. coli and brucite and palygorskite can help to understand the effect of fibrous minerals on microeubiosis of human normal flora and the contribution of microbial behaviors on the fibrous minerals weathering in the natural environment.

A novel method to harvest Chlorella sp. by co-flocculation/air flotation.

OBJECTIVES: To develop a more effective dissolved air flotation process for harvesting microalgae biomass, a co-flocculation/air flotation (CAF) system was developed that uses an ejector followed by a helix tube flocculation reactor (HTFR) as a co-flocculation device to harvest Chlorella sp. 64.01. RESULTS: The optimal size distribution of micro-bubbles and an air release efficiency of 96 % were obtained when the flow ratio of inlet fluid (raw water) to motive fluid (saturated water) of the ejector was 0.14. With a reaction time of 24 s in the HTFR, microalgae cells and micro-bubbles were well flocculated, and these aerated flocs caused a fast rising velocity (96 m/h) and high harvesting efficiency (94 %). CONCLUSIONS: In a CAF process, micro-bubbles can be encapsulated into microalgae flocs, which makes aerated flocs more stable. CAF is an effective approach to harvesting microalgae.

Methoxy-modified kaolinite as a novel carrier for high-capacity loading and controlled-release of the herbicide amitrole.

Methoxy-modified kaolinite was used as a novel carrier for loading and release of the herbicide 3-amino-1,2,4-triazole, known as amitrole (abbreviated here as AMT). The methoxy modification made the interlayer space of the kaolinite available for AMT intercalation. The AMT loading content in methoxy-modified kaolinite reached up to 20.8 mass% (twice the loading content by unmodified kaolinite). About 48% of this amount is located in the interlayer space. The release profiles of the AMT fit with the modified Korsmeyer-Peppas model. Due to the diffusional restriction of the intercalated AMT by the lamellar structure of the kaolinite and the strong electrostatic attraction between the intercalated AMT and the kaolinite, a slow release of AMT from the methoxy-modified kaolinite was achieved. These results show that the methoxy-modification is a facile method to make the interlayer space of kaolinite available for hosting other guest molecules. The methoxy-modified kaolinite is a promising candidate for high-capacity loading and controlled-release of other molecules such as drugs, agrochemicals, and biochemicals.

Nano-scale spatial assessment of calcium distribution in coccolithophores using synchrotron-based nano-CT and STXM-NEXAFS.

Calcified coccolithophores generate calcium carbonate scales around their cell surface. In light of predicted climate change and the global carbon cycle, the biomineralization ability of coccoliths has received growing interest. However, the underlying biomineralization mechanism is not yet well understood; the lack of non-invasive characterizing tools to obtain molecular level information involving biogenic processes and biomineral components remain significant challenges. In the present study, synchrotron-based Nano-computed Tomography (Nano-CT) and Scanning Transmission X-ray Microscopy-Near-edge X-ray Absorption Fine Structure Spectromicroscopy (STXM-NEXAFS) techniques were employed to identify Ca spatial distribution and investigate the compositional chemistry and distinctive features of the association between biomacromolecules and mineral components of calcite present in coccoliths. The Nano-CT results show that the coccolith scale vesicle is similar as a continuous single channel. The mature coccoliths were intracellularly distributed and immediately ejected and located at the exterior surface to form a coccoshpere. The NEXAFS spectromicroscopy results of the Ca L edge clearly demonstrate the existence of two levels of gradients spatially, indicating two distinctive forms of Ca in coccoliths: a crystalline-poor layer surrounded by a relatively crystalline-rich layer. The results show that Sr is absorbed by the coccoliths and that Sr/Ca substitution is rather homogeneous within the coccoliths. Our findings indicate that synchrotron-based STXM-NEXAFS and Nano-CT are excellent tools for the study of biominerals and provide information to clarify biomineralization mechanism.

Facile preparation of hierarchically porous carbon using diatomite as both template and catalyst and methylene blue adsorption of carbon products.

Hierarchically porous carbons were prepared using a facile preparation method in which diatomite was utilized as both template and catalyst. The porous structures of the carbon products and their formation mechanisms were investigated. The macroporosity and microporosity of the diatomite-templated carbons were derived from replication of diatom shell and structure-reconfiguration of the carbon film, respectively. The macroporosity of carbons was strongly dependent on the original morphology of the diatomite template. The macroporous structure composed of carbon plates connected by the pillar- and tube-like macropores resulted from the replication of the central and edge pores of the diatom shells with disk-shaped morphology, respectively. And another macroporous carbon tubes were also replicated from canoe-shaped diatom shells. The acidity of diatomite dramatically affected the porosity of the carbons, more acid sites of diatomite template resulted in higher surface area and pore volume of the carbon products. The diatomite-templated carbons exhibited higher adsorption capacity for methylene blue than the commercial activated carbon (CAC), although the specific surface area was much smaller than that of CAC, due to the hierarchical porosity of diatomite-templated carbons. And the carbons were readily reclaimed and regenerated.

FTIR spectroscopy study of the structure changes of palygorskite under heating.

Progressive heat treatment was applied to palygorskite, and the changes of the position and intensity of its infrared vibrations, particularly those in the low wavenumber region, were monitored by use of Fourier transform infrared spectroscopy. Moreover, the responses of the impurities in palygorskite under heating were also examined. Palygorskite is characterized by two bands at 1196 and 647 cm(-1), which are attributed to the asymmetric stretching vibration of the Si-O-Si group that connects the adjacent inverse SiO(4) tetrahedrons and the H(2)O-Mg-H(2)O stretching vibration in the MgO(6) octahedra at the edges of the channels, respectively. The band at approximately 680 cm(-1) is attributed to the overlapping symmetric stretching vibrations of Si-O-Mg and Si-O-Al (VI). In addition, the 865 cm(-1) band corresponds to the amorphous carbonate impurity.

Effects of inherent/enhanced solid acidity and morphology of diatomite templates on the synthesis and porosity of hierarchically porous carbon.

The inherent or enhanced solid acidity of raw or activated diatomite is found to have significant effects on the synthesis of hierarchically porous diatomite-templated carbon with high surface area and special porous structure. The solid acidity makes raw/activated diatomite a catalyst for the generation of porous carbon, and the porous parameters of the carbon products are strongly dependent on the solid acidity of diatomite templates. The morphology of diatomite also dramatically affects the textural structure of porous carbon. Two types of macroporous structures in the carbon product, the partially solid pillars and the ordered hollow tubes, derive from the replication of the central and the edge pores of diatom shell, respectively. The hierarchically porous carbon shows good capability for the adsorption of solvent naphtha and H(2), enabling potential applications in adsorption and gas storage.