Bentonite-supported nano zero-valent iron composite as a green catalyst for bisphenol A degradation: Preparation, performance, and mechanism of action.

Bisphenol A (BPA) is a toxic environmental pollutant commonly found in wastewater. Using non-toxic materials and eco-friendly technology to remove this pollutant from wastewater presents multiple advantages. Treatment of wastewater with clay minerals has received growing interest because of the environment friendliness of these materials. Bentonite is a 2:1 layered phyllosilicate clay mineral that can support nano-metal catalysts. It can prevent the agglomeration of nano-metal catalysts and improve their activity. In this article, a green catalytic nano zero-valent iron/bentonite composite material (NZVI@bentonite) was synthesized via liquid-phase reduction. The average size of NZVI was approximately 40-50 nm. Good dispersion and low aggregation were observed when NZVI was loaded on the surface or embedded into the nanosheets of bentonite. Degradation of BPA, a harmful contaminant widely found in wastewater at relatively high levels, by NZVI@bentonite was then investigated and compared with that by pristine NZVI through batch Fenton-like reaction experiments. Compared with pristine NZVI and bentonite alone, the NZVI@bentonite showed a higher BPA degradation ratio and offered highly effective BPA degradation up to 450 mg/g in wastewater under optimum operating conditions. Adsorption coupled with the Fenton-like reaction was responsible for BPA degradation by NZVI@bentonite. This work extends the application of NZVI@bentonite as an effective green catalyst for BPA degradation in aqueous environments.

Multivariate linear regression model for source apportionment and health risk assessment of heavy metals from different environmental media.

The study evaluated source apportionment of heavy metals in vegetable samples from the potential sources of fertilizer, water and soil samples collected along the Changjiang River delta in China. The results showed that 25.72% of vegetable samples (Brassica chinensis L.) containing Pb, and Cd, Cu, Hg and Zn at relatively serious levels were from soil. Combined with principle component analysis (PCA) and cluster analysis (CA), the results of the spatial distribution of heavy metals in different environmental media indicated that fertilizer, water and soil were the main sources of heavy metals in vegetables. The results of multivariate linear regression (MLR) using partition indexes (P) showed that fertilizer contributed to 38.5%, 40.56%, 46.01%, 53.34% and 65.25% of As, Cd, Cu, Pb and Zn contents in vegetables, respectively. In contrast, 44.58% of As, 32.57% of Hg and 32.83% of Pb in vegetables came from soil and 42.78% of Cd and 66.97% of Hg contents in vegetables came from the irrigation water. The results of PCA and CA verified that MLR using P was suitable for determining source apportionment in a vegetable. A health risk assessment was performed; As, Cd and Pb contributed to more than 75% of the total hazard quotient (THQ) values and total carcinogenic risk values (Risktotal) for adults and children through oral ingestion. More than 70% of the estimated THQ and Risktotal is contributed by water and fertilizer. Therefore, it is necessary to increase efforts in screening limits/levels of heavy metals in fertilizer and irrigation water and prioritize appropriate pollution management strategies.

Iron-containing nanominerals for sustainable phosphate management: A comprehensive review and future perspectives.

Adsorption, which is a quick and effective method for phosphate management, can effectively address the crisis of phosphorus mineral resources and control eutrophication. Phosphate management systems typically use iron-containing nanominerals (ICNs) with large surface areas and high activity, as well as modified ICNs (mICNs). This paper comprehensively reviews phosphate management by ICNs and mICNs in different water environments. mICNs have a higher affinity for phosphates than ICNs. Phosphate adsorption on ICNs and mICNs occurs through mechanisms such as surface complexation, surface precipitation, electrostatic ligand exchange, and electrostatic attraction. Ionic strength influences phosphate adsorption by changing the surface potential and isoelectric point of ICNs and mICNs. Anions exhibit inhibitory effects on ICNs and mICNs in phosphate adsorption, while cations display a promoting effect. More importantly, high concentrations and molecular weights of natural organic matter can inhibit phosphate adsorption by ICNs and mICNs. Sodium hydroxide has high regeneration capability for ICNs and mICNs. Compared to ICNs with high crystallinity, those with low crystallinity are less likely to desorb. ICNs and mICNs can effectively manage municipal wastewater, eutrophic seawater, and eutrophic lakes. Adsorption of ICNs and mICNs saturated with phosphate can be used as fertilizers in agricultural production. Notably, mICNs and ICNs have positive and negative effects on microorganisms and aquatic organisms in soil. Finally, this study introduces the following: trends and prospects of machine learning-guided mICN design, novel methods for modified ICNs, mICN regeneration, development of mICNs with high adsorption capacity and selectivity for phosphate, investigation of competing ions in different water environments by mICNs, and trends and prospects of in-depth research on the adsorption mechanism of phosphate by weakly crystalline ferrihydrite. This comprehensive review can provide novel insights into the research on high-performance mICNs for phosphate management in the future.

Electroplating wastewater treatment by in-situ formation of organic anions and inorganic anions intercalated layered double hydroxides.

The electroplating wastewater containing various metal ions was treated by adding sodium dodecyl benzene sulfonate (SDBS) and regulating pH value, and the resulting precipitates were characterized by X-ray diffraction (XRD). The results showed that organic anions intercalated layered double hydroxides (OLDHs) and inorganic anions intercalated layered double hydroxides (ILDHs) were in-situ formed to remove heavy metals during the treatment process. In order to reveal the formation mechanism of the precipitates, SDB- intercalated Ni-Fe OLDHs, NO3- intercalated Ni-Fe ILDHs and Fe3+-DBS complexes were synthsized by co-precipitation at various pH values for comparison. These samples were characterized by XRD, Fourier Transform infrared (FTIR), element analysis as well as the aqueous residual concentrations of Ni2+ and Fe3+ were detected. The results showed that OLDHs with good crystal structures can be formed as pH≤7, while ILDHs began to form at pH = 8. When pH < 7, complexes of Fe3+ and organic anions with the ordered layered structure were formed firstly, and then with increase in pH value, Ni2+ inserted into the solid complex and the OLDHs began to form. However, Ni-Fe ILDHs were not formed when pH ≤ 7. The Ksp (Solubility Product Constant) of OLDHs was calculated to be 3.24 × 10-19 and that of ILDHs was 2.98 × 10-18 at pH = 8, which suggested that OLDHs might be easier to form than ILDHs. The formation process of ILDHs and OLDHs were also simulated through MINTEQ software, and the simulation output verified that OLDHs could be easier to form than ILDHs at pH ≤ 7. Information from this study provides a theoretical basis for effective in-situ formation of OLDHs in wastewater treatment.

Environmental implication of geochemical record in the Arctic Ny-Ålesund glacial sediment, Svalbard (Norway).

Glacial sediments as an important end member of the global dust system, could indicate changes in global climate, aerosols sources, ocean elements, and productivity. With global warming, ice caps shrinking and glaciers retreat at high latitudes have attracted concern. To understand the response of glacier to environment and climate in modern high latitude ice-marginal environments, this paper investigated glacial sediments in the Ny-Ålesund region of the Arctic and clarified the response of polar environmental to global changes through geochemical characteristics of glacial sediments. The results showed that: 1) main factors affecting the elements distribution of the Ny-Ålesund glacial sediments were thought as soil formation, bedrock and weathering, and biological activity; 2) variations of SiO2/Al2O3 and SiO2/Al2O3 + Fe2O3, indicating low weathering of the soil. The ratio of Na2O/K2O indicating a weak chemical weathering, was negatively correlated to the CIA. With the average CIA of Ny-Ålesund glacial sediments for main minerals of quartz, feldspar, and muscovite as well as dolomite and calcite 50.13, which implied glacial sediments at the early stage of chemical weathering and depletion of Ca and Na; 3) the separating effect of stones and soils by stone circle formation due to thermal conductivity and frost heave makes sediments in stone circle have lower chemical weathering with only two main minerals, albite and quartz; 4) changes of carbonate content in sediments with glacier front retreating in different period implied that weathering rate of calcite averagely reached an estimate of 0.0792%wt/year in glacier A. The succession of vegetation made biological weathering become an important driving force for carbonate leaching from glacial sediments. These results and data provide scientifically significant archive for future global change studies.

Adsorption characteristics of assembled and unassembled Ni/Cr layered double hydroxides towards methyl orange.

The lamella aggregation state of layered double hydroxides (LDHs) may affect their sorption capacity for organic compounds. The dried LDH samples (Ni/Cr LDH-FA-D and Ni/Cr LDH-H2O-D) and the undried samples (Ni/Cr LDH-FA-W and Ni/Cr LDH-H2O-W) were flexibly prepared by a co-precipitation method in formamide (FA) and water, respectively. The results of X-ray diffraction (XRD) and transmission electron microscope (TEM) showed that the undried LDHs were unassembled, which had no the stacking layers but had a pseudohexagonal nanosheet lamella structure. And the unassembled LDH layers can be assembled again during the dry process. Ni/Cr LDH-FA-W and Ni/Cr LDH-H2O-W showed much greater adsorption capacities towards methyl orange (MO) than Ni/Cr LDH-FA-D and Ni/Cr LDH-H2O-D, as well as shorter time to reach equilibrium. The maximum adsorption capacity of MO could be calculated to 806 mg/g and 740 mg/g for Ni/Cr LDH-FA-W and Ni/Cr LDH-H2O-W by Langmuir-type simulation. The greater adsorption capacities of unassembled LDH could be attributed to the loosen structure and much more exposed adsorption sites. It could be concluded that unassembled LDHs were an effective and conducive preparation pathway for the exploration of the adsorption sites of LDHs.

Silylation of layered double hydroxides via a calcination-rehydration route.

Silylated layered double hydroxides (LDHs) were synthesized through a surfactant-free method involving an in situ condensation of silane with the surface hydroxyl group of LDHs during its reconstruction in carbonate solution. X-ray diffraction (XRD) patterns showed the silylation reaction occurred on the external surfaces of LDHs layers. The successful silylation was evidenced by (29)Si cross-polarization magic-angle spinning nuclear magnetic resonance ((29)Si CP/MAS NMR) spectroscopy, attenuated total reflection Fourier transform infrared (ATR FTIR) spectroscopy, and infrared emission spectroscopy (IES). The ribbon shaped crystallites with a "rodlike" aggregation were observed through transmission electron microscopy (TEM) images. The aggregation was explained by the T(2) and T(3) types of linkage between adjacent silane molecules as indicated in the (29)Si NMR spectrum. In addition, the silylated products show high thermal stability by maintained Si related bands even when the temperature was increased to 1000 degrees C as observed in IES spectra.

Investigation of inclusions trapped inside Libyan desert glass by Raman microscopy.

Several specimens of Libyan desert glass (LDG), an enigmatic natural glass from Egypt, were subjected to investigation by micro-Raman spectroscopy. The spectra of inclusions inside the LDG samples were successfully measured through the layers of glass and the mineral species were identified on this basis. The presence of cristobalite as typical for high-temperature melt products was confirmed, together with co-existing quartz. TiO(2) was determined in two polymorphic species rutile and anatase. Micro-Raman spectroscopy proved also the presence of minerals unusual for high-temperature glasses such as anhydrite and aragonite.

Use of autoclaved aerated concrete particles for simultaneous removal of nitrogen and phosphorus as filter media from domestic wastewater.

ABSTRACT In this study, autoclaved aerated concrete particles (AACPs) from construction waste were used to simultaneously remove phosphorus and nitrogen in biological aerated filters (BAFs). The effects of air/water (A/W) ratio on the removal performance of phosphorus (PO4 3-), total organic carbon, total nitrogen (TN), and ammonia nitrogen were investigated. Results showed that AACP BAF was more efficient than commercially available ceramsite (CAC) BAF. For example, the removal rates of TN with AACP and CAC were 45.96% and 15.64%, respectively, and those of PO4 3- with AACP and CAC were 72.45% and 33.97%, respectively, at the A/W ratio of 3:1. Different characterization methods were utilized to evaluate the surface shape, elemental compostion, and internal and surface structure of AACP. The interconnectivity and uniformity of pores and the rough surface of AACP were found to be suitable for the growth of microbial biofilm. In addition, the growth of internal pores in AACP promoted the removal of phosphorus and nitrogen. The surface of used AACP contained a small amount of irregular crystals and was covered with a layer of aggregates, which were characterized as hydroxyapatite [HAP, Ca5(OH)(PO4)3]. The formation of HAP as a final byproduct confirmed the successful removal of phosphorus. Therefore, construction wastes, such as AACPs, could be recycled and utilized as a promising biofilter media for excellent wastewater treatment.

XRD, TEM and thermal analysis of yttrium doped boehmite nanofibres.

Yttrium doped boehmite nanofibres with varying yttrium content have been prepared at low temperatures using hydrothermal treatment in the presence of the surfactant polyethylene oxide (PEO). The resultant nanofibres were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis. TEM images showed the resulting nanostructures are predominantly nanofibres when Y doping is less than 5%. When the doping was at the 10 or 20% content Y(OH)3 nanorods were formed. The nanorods show similar morphology to GaO(OH) nanorods. The doped boehmite and the subsequent nanofibres were analyzed by thermogravimetric and differential thermogravimetric methods. The boehmite nanofibres produced thermally transform at higher temperatures than boehmite crystals and boehmite platelets. In general two thermal decomposition steps are observed at around 45 and 379 degrees C assigned to dehydration and dehydroxylation. The dehydration step is attributed to interstitial water trapped between the boehmite layers. The dehydroxylation steps in the boehmite samples with doping above 3% are strongly asymmetric and additional peaks are resolved in the thermal analysis patterns. This peak becomes clear in the 10 and 20% Y doped boehmite samples and is attributed to the thermal decomposition of the Y(OH)3 nanorods.

Absorption of the selenite anion from aqueous solutions by thermally activated layered double hydroxide.

The presence of selenite or selenate in potable water is a health hazard especially when consumed over a long period of time. Its removal from potable water is of importance. This paper reports technology for the removal of selenite from water through the use of thermally activated layered double hydroxides. Mg/Al hydrotalcites with selenite in the interlayer were prepared at different times from 0.5 to 20 h through ion exchange. X-ray diffraction of the MgAlSeO3 hydrotalcites indicates that the selenite anion entered the interlayer spacing of Mg/Al hydrotalcite and MgAlSeO3 hydrotalcite was formed. Raman spectra proved the presence of selenite anion in the hydrotalcite interlayer as the counter anion. The band intensity and width of MgAlSeO3 hydrotalcite in the region of 3800-3000 cm(-1) increase with the adsorption of selenite by the Mg/Al hydrotalcite. The characteristic bands of free selenite anions in the MgAlSeO3 hydrotalcites are located between the region between 850 and 800 cm(-1). The Raman spectra of the lower wave number region of 550-500 cm(-1) show a shift toward higher wave numbers with adsorption of the selenite. An estimation of the amount of selenite anion removed by the thermally activated layered double hydroxide was obtained through the measurement of the intensity of the selenite Raman bands at 814 and 835 cm(-1) resulting from the amount of selenite anion remaining in solution. Thermally activated LDHs provide a mechanism for removing selenite anions from aqueous solutions.

Raman and infrared spectroscopy of arsenates of the roselite and fairfieldite mineral subgroups.

Raman spectroscopy complimented with infrared spectroscopy has been used to determine the molecular structure of the roselite arsenate minerals of the roselite and fairfieldite subgroups of formula Ca(2)B(AsO(4))(2).2H(2)O (where B may be Co, Fe(2+), Mg, Mn, Ni and Zn). The Raman arsenate (AsO(4))(2-) stretching region shows strong differences between the roselite arsenate minerals which is attributed to the cation substitution for calcium in the structure. In the infrared spectra complexity exists with multiple (AsO(4))(2-) antisymmetric stretching vibrations observed, indicating a reduction of the tetrahedral symmetry. This loss of degeneracy is also reflected in the bending modes. Strong Raman bands around 450 cm(-1) are assigned to nu(4) bending modes. Multiple bands in the 300-350 cm(-1) region assigned to nu(2) bending modes provide evidence of symmetry reduction of the arsenate anion. Three broad bands for roselite are found at 3450, 3208 and 3042 cm(-1) and are assigned to OH stretching bands. By using a Libowitzky empirical equation hydrogen bond distances of 2.75 and 2.67 A are estimated. Vibrational spectra enable the molecular structure of the roselite minerals to be determined and whilst similarities exist in the spectral patterns, sufficient differences exist to be able to determine the identification of the minerals.

Tlapallite H(6)(Ca,Pb)(2)(Cu,Zn)(3)SO(4)(TeO(3))(4)TeO(6), a multi-anion mineral: A Raman spectroscopic study.

Tellurates may be subdivided according to formula and structure. There are three types of tellurate minerals: type (a) (AB)(m)(TeO(4))(p)Z(q), type (b) (AB)(m)(TeO(6)).xH(2)O and type (c), compound tellurates in which a second anion is involved. Tlapallite, a multi-anion mineral containing both tellurate and tellurite units, as well as sulphate, is an example of type (a). Tellurates are rare minerals as the tellurate ion is easily reduced to the tellurite ion. Raman bands at 691, 708, 764 and 796cm(-1) are attributed to (TeO(6))(2-) and (TeO(3))(2-) stretching bands. The intense sharp Raman band at 973cm(-1) is assigned to the nu(1) (SO(4))(2-) symmetric stretching mode, whilst the two bands at 1062 and 1104cm(-1) are assigned to the nu(3) (SO(4))(2-) antisymmetric stretching mode. The spectral region 100 to 600cm(-1) displays the bands which are attributable to the (SO(4))(2), (TeO(3))(2-) and (TeO(6))(4-) bending modes. Some evidence from very low intensity Raman bands in the 2800-3600cm(-1) region provides evidence of proton-tellurate/tellurite anion interactions.

Near- and mid-infrared spectroscopy of the uranyl selenite mineral haynesite (UO2)3(SeO3)2(OH)2.5H2O.

Near- and mid-infrared spectra of uranyl selenite mineral haynesite (UO(2))(3)(SeO(3))(2)(OH)(2).5H(2)O, were studied and assigned. Observed bands were assigned to the stretching vibrations of uranyl and selenite units, stretching, bending and libration modes of water molecules and hydroxyl ions, and delta U-OH bending vibrations. U-O bond lengths in uranyl and hydrogen bond lengths O-H...O were inferred from the spectra.

Raman spectroscopic study of the tellurite minerals: mackayite and quetzalcoatlite.

Tellurites may be subdivided according to formula and structure. There are five groups based upon the formulae: (a) A(XO(3)), (b) A(XO(3)).xH(2)O, (c) A(2)(XO(3))(3).x(2)O, (d) A(2)(X(2)O(5)) and (e) A(X(3)O(8)). Raman spectroscopy has been used to study mackayite and quetzalcoatlite are examples of tellurites containing OH units Raman bands for mackayite observed at 732, 782 and 579, 635cm(-1) are assigned to the nu(1) (Te(2)O(5))(2-) symmetric stretching and nu(3) (Te(2)O(5))(2-) antisymmetric stretching modes. The Raman spectral profile of quetzalcoatlite is more complex with a considerable number of overlapping bands. Two bands may be resolved at 719 and 754cm(-1) which may be attributed to nu(1) (Te(2)O(5))(2-) symmetric stretching mode. The two Raman bands of quetzalcoatlite at 602 and 606cm(-1) are accounted for by the nu(3) (Te(2)O(5))(2-) antisymmetric stretching mode. Raman bands for mackayite, observed at 306, 349, 379 and 424, 436cm(-1) are assigned to the (Te(2)O(5))(2-) nu(2) (A(1)) bending mode and nu(4) (E) bending modes. This research shows that Raman spectroscopy may be applied to tellurite minerals successfully.

Raman spectroscopic study of the tellurite mineral: rodalquilarite H3Fe2(3+)(Te4+O3)4Cl.

Tellurites may be subdivided according to formula and structure. There are five groups based upon the formulae (a) A(XO3); (b) A(XO3).xH2O; (c) A2(XO3)3.xH2O; (d) A2(X2O5) and (e) A(X3O8). Rodalquilarite, a tellurite mineral of type (a) has been studied using Raman spectroscopy. Observed from the spectra was the presence of protons, an essential stabilising element for the minerals structure and stability. The tellurite ion should show a maximum of six bands. The free tellurite ion shows C3v symmetry and has four modes, 2A1 and 2E. Three Raman bands at 726, 755 and 780 cm(-1) are assigned to the nu1 (TeO3)2- symmetric stretching mode and the two bands at 610 and 642 cm(-1) are attributed to the nu3 (TeO3)2- antisymmetric stretching mode. The two bands at 321 and 345 cm(-1) and the two bands at 449 and 473 cm(-1) are assigned to the (TeO3)2-nu2 (A1) bending mode and (TeO3)2-nu4 (E) bending mode. Raman bands observed at 2341, 2796 and 2870 cm(-1) are attributed to OH stretching vibrations caused by interaction between the protons and the oxygen of the tellurite units. The values for these OH stretching vibrations provide hydrogen bond distances of 2.550 (6) A (2341 cm(-1)), 2.610 (3) A (2796 cm(-1)) and 2.623 (2) A (2870 cm(-1)) which are comparatively short for secondary minerals.

Raman spectroscopic study of the tellurite minerals: carlfriesite and spiroffite.

Raman spectroscopy has been used to study the tellurite minerals spiroffite and carlfriesite, which are minerals of formula type A(2)(X(3)O(8)) where A is Ca(2+) for the mineral carlfriesite and is Zn(2+) and Mn(2+) for the mineral spiroffite. Raman bands for spiroffite observed at 721 and 743 cm(-1), and 650 cm(-1) are attributed to the nu(1) (Te(3)O(8))(2-) symmetric stretching mode and the nu(3) (Te(3)O(8))(2-) antisymmetric stretching modes, respectively. A second spiroffite mineral sample provided a Raman spectrum with bands at 727 cm(-1) assigned to the nu(1) (Te(3)O(8))(2-) symmetric stretching modes and the band at 640cm(-1) accounted for by the nu(3) (Te(3)O(8))(2-) antisymmetric stretching mode. The Raman spectrum of carlfriesite showed an intense band at 721 cm(-1). Raman bands for spiroffite, observed at (346, 394) and 466 cm(-1) are assigned to the (Te(3)O(8))(2-)nu(2) (A(1)) bending mode and nu(4) (E) bending modes. The Raman spectroscopy of the minerals carlfriesite and spiroffite are difficult because of the presence of impurities and other diagenetically related tellurite minerals.

Raman spectroscopic study of the uranyl minerals vanmeersscheite U(OH)4[(UO2)3(PO4)2(OH)2].4H2O and arsenouranylite Ca(UO2)[(UO2)3(AsO4)2(OH)2].(OH)2.6H2O.

Raman and infrared spectra of secondary uranyl phosphate vanmeersscheite and Raman spectrum of secondary uranyl arsenate arsenuranylite were recorded and interpreted, and the spectra related to the structure of the minerals. Observed bands were attributed to the stretching and bending vibrations of uranyl, phosphate and/or arsenate units and OH (H(2)O and OH(-)) units. Phosphuranylite sheet topology is characteristic for both minerals. U-O bond lengths in uranyl were calculated from the spectra and compared with those inferred for vanmeersscheite from the X-ray single crystal structure analysis. O-H...O hydrogen bonds in both minerals were also inferred using the Libowitzky empirical relation.

Characterisation of red mud by UV-vis-NIR spectroscopy.

The characterisation of red mud has been studied by diffuse reflectance spectroscopy in the UV-vis-NIR region (DRS). For the first time the ferric ion responsible for the bands has been identified from electronic spectroscopy. It contains valuable amounts of oxidised iron (Fe(3+)) and aluminium hydroxide. The NIR peak at around 11,630 cm(-1) (860 nm) with a split of two components and a pair of sharp bands near 500 nm (20000 cm(-1)) in the visible spectrum are attributed to Fe(3+) ion in distorted sixfold coordinations. The observation of identical spectral patterns (both electronic and vibrational spectra) of red mud before and after seawater neutralisation (SWN) confirmed that there is no effect of seawater neutralisation on structural cation substitutions such as Al(3+), Fe(3+), Fe(2+), Ti(3+), etc.

Characterisation of Ni silicate-bearing minerals by UV-vis-NIR spectroscopy. Effect of Ni substitution in hydrous Ni-Mg silicates.

Three Ni silicate-bearing pimelite, nepouite and pecoraite minerals, from Australia have been investigated by UV-vis-NIR spectroscopy to study the effect of Ni-Mg substitution. The observation of three major absorption bands at 9205-9095, 15,600-15,190 and 26,550-25,660 cm(-1) are the characteristic features of Ni(2+) in sixfold coordination. The effect of cation substitution like Mg(2+) for Ni(2+) on band shifts in electronic and vibrational spectra enable the distinction between the Ni-bearing silicates.