Capturing Cu2+ and recycling spent Cu-adsorbents as catalyst for eliminating Rhodamine B: reactivity and mechanism.

The thorny problem of adsorption is the disposing of spent adsorbent. In this manuscript, the exhaust adsorbent of efficient capture Cu(II) over ZSM-5 that supported zero-valent iron (nZVI) was reused as a catalyst for eliminating Rhodamine B (RhB). Batch experiments were used to evaluate the removal performance of Cu2+ and RhB. The results demonstrated that the Cu2+ adsorption process obeyed pseudo-second-order kinetics, and the adsorption performance was dependent on solution pH. The maximum adsorption capacity at the optimal pH 4.0 was 375.9 mg/g; equilibrium was reached rapidly within 35 min. From XPS, the reduction-oxidation between Fe0 and Cu2+ was occurred in the adsorption process, and Fe2+, Fe3+, and Cu0 was formed. In the recycling experiments, RhB was removed by the spent Cu adsorbent, with the removal performance being dependent on the initial Cu concentration, in the order of 5 mg/L > 20 mg/L > 0 mg/L > 100 mg/L > 500 mg/L. RhB removal also improved with increasing H2O2 concentration. More than 99.9% of the RhB was degraded within 8 min using 1.75 mM H2O2, which was a large improvement over the previously used catalyst. The hydroxyl radical was found to be the main free radical responsible for RhB degradation.

Development of an H2S emission model for wastewater treatment plants.

Modeling and prediction of H2S emission from wastewater are important since gaseous H2S will induce significant corrosion and odor problems. Most previous studies focused on H2S emission of wastewater in pipeline systems, which may not be fit for H2S emission in wastewater treatment plants (WWTPs). This study provided a two-phase mass transfer model for prediction of H2S emission concentrations. The model is based on the mass transfer rate equation of the mass transfer impetus, expressed by the concentration difference. The main parameters of the model are the mass transfer coefficient, the carrier gas flow rate and the concentration of H2S in liquid phase. The results showed that the model can simulate and predict H2S emission concentrations of various processes in WWTPs. Moreover, the model can analyze and predict the influences of different pH values, mass transfer coefficients and carrier gas flow rates on H2S emission concentrations and loads. Therefore, the model provides theoretical guidance for design of WWTPs regarding H2S emissions.Implications: Modeling and prediction of H2S emission from wastewater are quite important since gaseous H2S will induce significant corrosion and odor problems. Most of previous studies are focused on H2S emission from wastewater in pipeline system, which may not be fit for H2S emission in wastewater treatment plants (WWTPs). Thus in this study, a model for predicting H2S emission from typical units of WWTPs is established and verified. Moreover, the influences of pH values, mass transfer coefficients and carrier gas flow rates on H2S emission are analyzed. The model can be a useful tool to predict the H2S concentration in odor gas collection system of WWTP and understand the behaviors of H2S emission under different WWTPs operating conditions.

Enhancing As(V) and As(III) adsorption performance of low alumina fly ash with ferric citrate modification: Role of FeSiO3 and monosodium citrate.

Fly ash and arsenic species have been regarded as contaminants that pollute the environment. Herein, low alumina fly ash (LAFA) was utilized to fabricate the As(V) and As(III) adsorbent via combining the routes of alkali fusion and incipient-wetness impregnation. The characterization results suggested that the grafted ferric citrate was coordinated to LAFA by substituting a Si4+ to a Fe3+, and the compound monosodium citrate was observed. Based on the XPS analysis, the C-O and -COO- groups of monosodium citrate played the significant role in uptaking As(V) and As(III) species by chemical complexation, the FeOOH adsorbed As(V) and As(III) species via ion-exchange, and the Fe2O3 oxidize As(III) into As(V). Additionally, it was observed that the As(V) removal performance by adsorbent prepared with different modifiers was in the order of FeC6H5O7 (ca. 93.7%) > C6H8O7 (84%) > HCl (73%). And then, the optimal adsorbent synthesis condition for As(V) uptake was explored at ferric citrate loaded LAFA with 1:1 mass ratio (fly ash to NaOH) under temperature 923 K. The maximum monolayer adsorption capacities of the optimal adsorbent were 2725.0 µgAs(V)/g and 2281.9 µgAs(III)/g, and the removal efficiency of As(V) and As(III) was near 100% for their initial concentrations below 500 ppb, where the residual arsenic concentration met the required standard in drinking water (lower than 10 ppb).

Solvent-free synthesis of MFI-type zeolites and their degradation properties of gas-phase styrene.

In this study, a series of MFI-type zeolites with various compositions were synthesized by a solvent-free synthesis method at a comparatively mild condition. The results of investigations showed that the as-synthesized samples displayed a good crystallinity grade and regular morphology of layered structure. The crystallization process of TS-1 was systematic investigated. It was revealed that the transition stage of crystallization process was the formation of nucleation intermediates (Na2SiF6), which was the key factor for dropping Ti atoms into MFI framework. Meanwhile, it showed a high apparent nucleation activation energy (64.8 kJ mol-1), and low growth activation energy (25.3 kJ mol-1) in a spontaneous nucleation system, and the nucleation activation energy could be reduced to 17.2 kJ mol-1 in non-spontaneous nucleation system. The as-synthesized zeolites were evaluated for their catalytic activity for the degradation of gas-phase styrene. The titanium silicalite-1 sample doped with iron exhibited excellent catalytic activity with 100% degradation of styrene. The method employed in this work not only decreases the production cost and energy-consumption of MFI-type zeolites, but also significantly enhances their production yield. Moreover, it is an efficient pathway to solve the pollution of volatile organic compounds using solid waste.

The adsorption behavior and mechanism of Cr(VI) on facile synthesized mesoporous NH-SiO2.

An efficient Cr(VI) adsorbent, mesoporous amine-functionalized silica (NH-SiO2), was successfully synthesized within 2 h by a facile one-step route under room temperature and aqueous solution. The structure properties of the obtained materials were characterized by N2 adsorption-desorption isotherm, XRD, TEM, and FT-IR. The Cr(VI) removal performance was investigated by batch experiment. It was found that Cr(VI) removal performance was dependent on solution pH, and the removal efficiency is above 90% for initial pH in the range of 1.0-4.0. The adsorption process was obeyed by pseudo-second-order model, and the equilibrium adsorption data were fitted well by Langmuir model. The maximum monolayer adsorption capacity was 205.76 mg/g at pH 2.0, which was larger than that of traditional two-step tri-amine-functionalized MCM-41. Additionally, high selectivity was exhibited in NH-SiO2 for removal Cr(VI) from co-presence anions Cl-, NO3-, PO43-, SO42-, and SiO32-. Furthermore, the spent NH-SiO2 could be regenerated by 0.005 M NaOH, and Cr(VI) removal is above 92% after NH-SiO2 recycled four. From the analyzed results of adsorption energy, FT-IR, and XPS, the electrostatic attraction between protonated amine group and HCrO4- was the mainly adsorption mechanism. And then some adsorbed Cr(VI) was reduced to low toxicity Cr(III) on the adsorbent surface by electron transfer from nitrogen in -NBr group to Cr(VI).

Removal performance and mechanisms of Cr(VI) by an in-situ self-improvement of mesoporous biochar derived from chicken bone.

A high-performance mesoporous biochar (MBCX) was fabricated from chicken bone via a facile and low-energy consumption pyrolysis process without any additional activators and templates. The physicochemical properties of biochar were carried out by elemental compositions, N2 adsorption-desorption isotherms, FTIR, and TG. The results illustrated that lower carbonization temperature leaded to a lower specific surface area and more polar functional groups. And the meso-structure of biochar was obtained at 350 °C. Combined with the result of batch experiment, Cr(VI) adsorption capacity was decreased with the increasing in pyrolysis temperature, which suggested that the removal performance was depended on the functional groups of mesoporous biochar rather than the surface area. Kinetic analysis showed that the Cr(VI) adsorption process on MBCX was suitable for Elovich kinetic. The experimental data was well explained by Langmuir isotherm models. And the maximum adsorption capacity was 58.195 mg/g, which was higher than that of most report pristine biochars. This work not only paved a way for subsequent mesoporous biochar preparation but also demonstrated the application potentials of MBCX as an environment benign Cr(VI) adsorbent.

The identification of active chromium species to enhance catalytic behaviors of alumina-based catalysts for sulfur-containing VOC abatement.

As to the treatment of sulfur containing VOCs (examples are compounds of CH3SH and C2H5SH), finding a catalyst with high performance is necessary. In this work, Cr(x)-Al2O3 (x = 1.0, 2.5, 5.0, 7.5 and 10 wt%) catalysts were synthesized, and their behaviors toward CH3SH and C2H5SH abatement were investigated. The results indicated that Cr(7.5)-Al2O3 exhibited higher activity than other samples and the reported catalysts, on which CH3SH could be almost completely converted at 375 °C, while the temperature for the reported catalysts was above 450 °C. Moreover, there was no obvious deactivation during 30 h on stream over Cr(7.5)-Al2O3, while only about 10 h was found on the reported CeO2 and HZSM-5 catalysts. The improvement in the catalytic performance could be explained by the important role of the Cr6+ species, while the state of Cr3+ was suggested to be ineffective in the degradation process. The identification of the active Cr sites was proved by the characterization measurements, and the control experiments by using mechanical mixtures of CrO3 or Cr2O3 with Al2O3 as well as the comparison studies between spent Al2O3 and spent Cr(7.5)-Al2O3 catalysts.

Microwave assistant rapid synthesis MCM-41-NH2 from fly ash and Cr(VI) removal performance.

Synthesis of silicon materials from fly ash is an ecologically justified process aimed at the transformation of energy sector waste-fly ash into mesoporous silicon material of broad possible application field. In this study, the MCM-41-NH2 was successfully synthesized from industrial solid waste fly ash via a facile and fast process of alkali fusion method under the assistant of microwave. Due to the employ of microwave, the aging time was controlled within 30 min, which was significantly shorter than that of traditional hydrothermal method (48-72 h). And, the obtained MCM-41-NH2 was shown an excellent performance to remove Cr(VI) from solution under the investigation of fixed-bed column. The maximum adsorption capacity for Cr(VI) was 53.77 mg/g. Additionally, the effect of initial concentration, flow rate, bed height, and pH on Cr(VI) removal were investigated, and the models of Thomas and Adams-Bohart were applied to predict the experiment data; the correlation coefficients (R2) of Thomas model under the investigated conditions were all close to 1. Furthermore, the adsorbent was characterized by N2 adsorption-desorption isotherm, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential, ultraviolet-visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), and NH3-Temperature Programmed Desorption (NH3-TPD). The results showed that amino groups play an important role in the adsorption process. Cr(VI) was firstly adsorbed on the surface of the MCM-41-NH2, and then some of the adsorbed Cr(VI) were reduced to Cr(III) by the release of the protons of the ammonium. The information showed that MCM-41-NH2 could be an effective and low-cost sorbent for removing Cr(VI) from wastewater. Furthermore, recycling experiments showed that the spent adsorbent had high catalytic performance for methyl mercaptan (CH3SH). Graphical abstract .

Facile synthesis of amino-functional large-size mesoporous silica sphere and its application for Pb2+ removal.

Amino-functional large-size mesoporous silica spheres (LMS-AP) were successfully synthesized through a one-step method with (3-aminopropyl) triethoxysilane (APTES) addition during the pseudomorphic transformation process. LMS-AP were characterized using thermogravimetry-differential thermal analysis, Nitrogen adsorption-desorption measurement, infrared spectroscopy, and X-ray photoelectron spectroscopy. The study found that -NH2 was grafted into LMS, and the LMS-AP had a better thermal stability than other samples. The Pb2+ removal properties of LMS-AP were investigated using the static and dynamic experiments in simulated and real wastewater solutions. The kinetic and equilibrium experiments indicated that the adsorption process of LMS-AP fitted the Langmuir adsorption model and the pseudo-second-order kinetics model (R2 > 0.98), respectively. The maximum Qe (mg/g) was about 100 mg/g in the static adsorption condition. The adsorption mechanism of removal of Pb2+ was also investigated. In fix bed column experiments, LMS-AP exhibited excellent Pb2+ adsorption ability for simulated wastewater, with the maximum qe (mg/g) of 48.7 mg/g for particle size under 1-3 mm. Meanwhile in actual industrial wastewater treatment process, LMS-AP had a better Pb2+, Zn2+ and Cr (VI) removal efficiency of 80% and As (V) of 30-40% removal efficiency at initial pH 4, suggesting selective adsorption property for different heavy metal ions.

Characterizations and mechanisms for synthesis of chitosan-coated Na-X zeolite from fly ash and As(V) adsorption study.

Solid waste fly ash with low aluminum of Yunnan Province in China was used as pristine material to prepared chitosan-coated Na-X zeolite, and the obtained composite material was employed as As(V) adsorbent. Then, the prepared materials were characterized by XRD, FT-IR, and XPS. And the results suggested that the low aluminum fly ash was successfully convert into Na-X zeolite, and the mineralization between Si-OH of the obtained Na-X zeolite and C-OH of chitosan was the dominated mechanism for coated chitosan over the surface of Na-X zeolite. From the batch experiments of As(V) removal, it has been found that the coated chitosan could significantly improve As(V) performance of Na-X zeolite. The optimal working pH for removal As(V) by chitosan-coated Na-X zeolite was attained at pH 2.1 ± 0.1, and the maximum adsorption capacity was 63.23 mg/g. And the adsorption data at different interval time was excellent fitted by pseudo-second-order kinetic model. From the analyze of XPS, the results suggested that As(V) uptake over adsorbent by the bond of As-N and As-O and the surface hydroxyl group of Al-OH and -NH2 were involved in uptake As(V) from acid wastewater.

Separate As(V) from solution by mesoporous Y-Al binary oxide: batch experiments.

Contaminant arsenic(V) has been regarded as one of the top-priority pollutants to remove from water. In this contribution, different mesoporous Y-Al binary oxides were prepared by the wet impregnation method via varying the molar ratio of Y/Al in the range of 0.029 to 0.116. The manufactured materials were employed as adsorbent to separate arsenic(V) from water. The adsorbent was characterized by N2 adsorption-desorption isotherm, point of zero charge (PZC) and Fourier transform infrared (FT-IR). Furthermore, the effect of experimental parameters on adsorption performance was evaluated by batch experiments, including the molar ratio of Y/Al, adsorbent dosages and contact time, initial concentration, initial pH and temperature. The results indicated that the adsorbent presented an optimal adsorption performance for As(V) uptake when the molar ratio of Y/Al was 0.058. The obtained experimental data were best fitted by Langmuir isotherm and the maximum adsorption capacity was 60.93 mg/g at pH 6.6 ± 0.1. Additionally, according to the results of adsorption kinetics, it was pronounced that adsorption process was complied with pseudo-second-order model. The adsorption thermodynamic suggested that the adsorption of As(V) is endothermic and spontaneous natural. Moreover, based on the results of FT-IR, PZC and initial pH, it is demonstrated that ion-exchange and electrostatic interaction were the dominating adsorption mechanism.

Investigating the Heavy Metal Adsorption of Mesoporous Silica Materials Prepared by Microwave Synthesis.

Mesoporous silica materials (MSMs) of the MCM-41 type were rapidly synthesized by microwave heating using silica fume as silica source and evaluated as adsorbents for the removal of Cu2+, Pb2+, and Cd2+ from aqueous solutions. The effects of microwave heating times on the pore structure of the resulting MSMs were investigated as well as the effects of different acids which were employed to adjust the solution pH during the synthesis. The obtained MCM-41 samples were characterized by nitrogen adsorption-desorption analyses, X-ray powder diffraction, and transmission electron microscopy. The results indicated that microwave heating method can significantly reduce the synthesis time of MCM-41 to 40 min. The MCM-41 prepared using citric acid (c-MCM-41(40)) possessed more ordered hexagonal mesostructure, higher pore volume, and pore diameter. We also explored the ability of c-MCM-41(40) for removing heavy metal ions (Cu2+, Pb2+, and Cd2+) from aqueous solution and evaluated the influence of pH on its adsorption capacity. In addition, the adsorption isotherms were fitted by Langmuir and Freundlich models, and the adsorption kinetics were assessed using pseudo-first-order and pseudo-second-order models. The intraparticle diffusion model was studied to understand the adsorption process and mechanism. The results confirmed that the as-synthesized adsorbent could efficiently remove the heavy metal ions from aqueous solution at pH range of 5-7. The adsorption isotherms obeyed the Langmuir model, and the maximum adsorption capacities of the adsorbent for Cu2+, Pb2+, and Cd2+ were 36.3, 58.5, and 32.3 mg/g, respectively. The kinetic data were well fitted to the pseudo-second-order model, and the results of intraparticle diffusion model showed complex chemical reaction might be involved during adsorption process.

Identification and characterization of a pyridoxal 5'-phosphate phosphatase in the silkworm (Bombyx mori).

Vitamin B6 comprises six interconvertible pyridine compounds, among which pyridoxal 5'-phosphate (PLP) is a coenzyme for over 140 enzymes. PLP is also a very reactive aldehyde. The most well established mechanism for maintaining low levels of free PLP is its dephosphorylation by phosphatases. A human PLP-specific phosphatase has been identified and characterized. However, very little is known about the phosphatase in other living organisms. In this study, a cDNA clone of putative PLP phosphatase was identified from B. mori and characterized. The cDNA encodes a polypeptide of 343 amino acid residues, and the recombinant enzyme purified from E. coli exhibited properties similar to that of human PLP phosphatase. B. mori has a single copy of the PLPP gene, which is located on 11th chromosome, spans a 5.7kb region and contains five exons and four introns. PLP phosphatase transcript was detected in every larva tissue except hemolymph, and was most highly represented in Malpighian tube. We further down-regulated the gene expression of the PLP phosphatase in 5th instar larvae with the RNA interference. However, no significant changes in the gene expression of PLP biosynthetic enzymes and composition of B6 vitamers were detected as compared with the control.

An interpenetrated bioactive nonlinear optical MOF containing a coordinated quinolone-like drug and Zn(II) for pH-responsive release.

A new interpenetrated bioactive nonlinear optical metal-organic framework [Zn2(ppa)2(1,3-bdc)(H2O)] has been designed and synthesized, which shows both a high drug content of 63.9% and a good slow release effect in simulated physical conditions compared to other non-interpenetrated bioactive MOFs. It also shows a large powder second-harmonic generation (SHG) efficiency of 5.6 times that of KH2PO4 (particle size: 150-200 µm).

Tuning of valence States, bonding types, hierarchical structures, and physical properties in copper/halide/isonicotinate system.

Seven cupric halide coordination polymers, namely [Cu5(OH)3Br3(ina)4] (1), [Cu5(OH)3Cl3(ina)4] (2), [Cu2(OH)Cl(ina)2] (3), [Cu3(OH)2Cl2(ina)2]·2H2O (4), [Cu3(OH)2Br2(ina)2]·2H2O (5), [Cu2Cl2(ina)2(H2O)2] (6), [Cu2Cl(ina)2(gca)(H2O)] (7), cupric complex templated cuprous halide [Cu(II)(Me-ina)2(H2O)][Cu(I)5Br7] (8), and organic templated cuprous halide Me2-ina[Cu2Br3] (9) (Hina = isonicotinic acid), were prepared from the starting materials of cupric halide and Hina via fine-tuning solvothermal reactions. According to valence states of copper, 1-7 are copper(II) complexes, 8 is a mixed-valent Cu(I,II) complex, while 9 is a Cu(I) compound. According to bonding types of halides, nine complexes can be classified as three types: complexes 1-3 include only normal X-Cu bond (X = halide); complexes 4-7 include normal X-Cu bond and X···Cu weak bond; complexes 8 and 9 include normal X-Cu bond and X···H-C halogen hydrogen bonds. Complexes 1 and 2 are isomorphic three-dimensional (3D) pcu topological metal organic frameworks (MOFs) with butterfly-like Cu4(µ3-OH)2X2 and steplike Cu6(µ3-OH)4 cores as nodes, showing strong ferromagnetic couplings. Complex 3 also is a pcu topological MOF with only butterfly-like Cu4(µ3-OH)2Cl2 clusters as nodes, presenting spin canting antiferromagnetic behavior. Isostructural 4 and 5 are Cu3(OH)2 clusters based two-dimensional (2D) (4,4) layers, which are extended into 3D eight-connected networks via weak Cu···X bonds, showing ferromagnetic coupling. Antiferromagnetic 6 is a simple one-dimensional coordination polymer, which is extended via weak Cu···Cl bonds into 3D (3,4)-connected networks. Paramagnetic 7 is a ladderlike polymer, which is extended into 2D (3,4)-connected layer via weak Cu···Cl bonds. The syntheses of polymeric cupric complexes 1-7 mainly result from differences in reactant ratio and pH value. Utilization of reducing methanol generated novel cubane-containing [Cu5Br7](2-) chain templated by paddlewheel-like [Cu(II)(Me-ina)2](2+) 8 and face-shared dimer-containing [Cu2Br3](-) chain templated by N-methylated and O-esterificated Me2-ina 9. Complex 9 exhibits a strong red emission and a weaker green emission upon excitation.

Poly[tetra-methyl-ammonium [tri-µ2-formato-κ(6) O:O'-manganate(II)]].

In the title compound, {(C4H12N)[Mn(HCO2)3]} n , the Mn(II) atom lies on an inversion centre and is coordinated by O-atom donors from the three double-bridging formate ligands, one of which lies across a crystallographic mirror plane, giving a slightly distorted octahedral coordination sphere. A three-dimensional NaCl-type framework is generated in which the tetra-methyl-ammonium cations, which lie across mirror planes and occupy the cavities in the polymer structure, form weak C-H⋯O hydrogen bonds with the formate ligands.

The optimization of As(V) removal over mesoporous alumina by using response surface methodology and adsorption mechanism.

The Box-Behnken Design of the response surface methodology was employed to optimize four most important adsorption parameters (initial arsenic concentration, pH, adsorption temperature and time) and to investigate the interactive effects of these variables on arsenic(V) adsorption capacity of mesoporous alumina (MA). According to analysis of variance (ANOVA) and response surface analyses, the experiment data were excellent fitted to the quadratic model, and the interactive influence of initial concentration and pH on As(V) adsorption capacity was highly significant. The predicted maximum adsorption capacity was about 39.06 mg/g, and the corresponding optimal parameters of adsorption process were listed as below: time 720 min, temperature 52.8 °C, initial pH 3.9 and initial concentration 130 mg/L. Based on the results of arsenate species definition, FT-IR and pH change, As(V) adsorption mechanisms were proposed as follows: (1) at pH 2.0, H3AsO4 and H2AsO4(-) were adsorbed via hydrogen bond and electrostatic interaction, respectively; (2) at pH 6.6, arsenic species (H2AsO4(-) and HAsO4(2-)) were removed via adsorption and ion exchange, (3) at pH 10.0, HAsO4(2-) was adsorbed by MA via ion exchange together with adsorption, while AsO4(3-) was removed by ion exchange.