Novel BiOI/BiOBr heterojunction photocatalysts with enhanced visible light photocatalytic properties

A novel heterojunction photocatalyst BiOI/BiOBr was synthesized by a simple modified deposition–precipitation method. Several characterization tools including XRD, SEM, HRTEM and UV–vis DRS were employed to study the phase structures, morphologies and optical properties of the samples. BiOI/BiOBr exhibited higher photocatalytic activity than single BiOI and BiOBr for the degradation of methyl orange (MO) under visible light (λ > 420 nm). This result can be due to the formation of the heterojunction between BiOI and BiOBr, which can separate photogenerated carriers efficiently. The photocatalytic mechanism study demonstrates that O₂⁻ and h⁺ are the main reactive species while OH can be negligible.     

Characteristics of the mercury vapor removal from coal combustion flue gas by activated carbon using H2S

Removal of Hg⁰ vapor from the simulated coal combustion flue gases with a commercial activated carbon was investigated using H₂S. This method is based on the reaction of H₂S and Hg over the adsorbents. The Hg⁰ removal experiments were carried out in a conventional flow type packed bed reactor system in the temperature range of 80–150 °C using simulated flue gases having the composition of Hg⁰ (4.9 ppb), H₂S (0–20 ppm), SO₂ (0–487 ppm), CO₂ (10%), H₂O (0–15%), O₂ (0–5%), N₂ (balance gas). The following results were obtained: in the presence of both H₂S and SO₂, Hg removal was favored at lower temperatures (80–100 °C). At 150 °C, presence of O₂ was indispensable for Hg⁰ removal from H₂S–SO₂ flue gas system. It is suggested that the partial oxidation of H₂S with O₂ to elemental sulfur (H₂S+1/2O₂=S_ad+H₂O) and the Clause reaction (SO₂+2H₂S=3S_ad+2H₂O) may contribute to the Hg⁰ removal over activated carbon by the following reaction: S_ad+Hg=HgS. The formation of elemental sulfur on the activated carbon was confirmed by a visual observation.     

Visible-light-responsive photocatalysts xBiOBr–(1−x)BiOI

A new class of oxyhalide photocatalysts xBiOBr–(1−x)BiOI prepared by a soft chemical method were characterized by X-ray diffraction and UV–Vis diffuse reflectance spectra. They are all visible-light-responsive materials with the bandgaps ranging from 1.92 to 2.91 eV. Methyl orange (MO) photocatalytic degradation experiments showed that BiOBr possessed a higher photocatalytic activity than P25 (TiO₂) under UV illumination and iodine-modified BiOBr exhibited high photocatlytic activities under visible-light irradiation. The high photocatalytic activity is in close relation with the deep valance band edge position and the internal electric fields between [Bi₂O₂] slabs and halogen anionic slabs.     

Mercury oxidation by hydrochloric acid over TiO2 supported metal oxide catalysts in coal combustion flue gas

Mercury oxidation by hydrochloric acid over the metal oxides supported by anatase type TiO₂ catalysts, 1 wt.% MO_x/TiO₂ where M = V, Cr, Mn, Fe, Ni, Cu, and Mo, was investigated by the Hg⁰ oxidation and the NO reduction measurements both in the presence and absence of NH₃. The catalysts were characterized by BET surface area measurement and Raman spectroscopy. The metal oxides added to the catalyst were observed to disperse well on the TiO₂ surface. For all catalysts studied, the Hg⁰ oxidation by hydrochloric acid was confirmed to proceed. The activity of the catalysts was found to follow the trend MoO₃ ~ V₂O₅ > Cr₂O₃ > Mn₂O₃ > Fe₂O₃ > CuO > NiO. The Hg⁰ oxidation activity of all catalysts was depressed considerably by adding NH₃ to the reactant stream. This suggests that the metal oxide catalysts undergo the inhibition effect by NH₃. The activity trend of the Hg⁰ oxidation in the presence of NH₃ was different from that observed in its absence. A good correlation was found between the NO reduction and the Hg⁰ oxidation activities in the NH₃ present condition. The catalyst having high NO reduction activity such as V₂O₅/TiO₂ showed high Hg⁰ oxidation activity. The result obtained in this study suggests that the oxidation of Hg⁰ proceeds through the reaction mechanism, in which HCl competes for the active catalyst sites against NH₃. NH₃ adsorption may predominate over the adsorption of HCl in the presence of NH₃.     

Synthesis of a carbamide-based dithiocarbamate chelator for the removal of heavy metal ions from aqueous solutions

This study was carried out to develop a carbamide-based dithiocarbamate (CDTC) chelator for the removal of heavy metal ions from wastewater. Its structural properties were characterized by FT-IR, ¹H NMR and ¹³C NMR. Results confirmed the functional groups of HNC(S)S existed. The adsorption isotherms showed CDTC had a high adsorption capability for Zn (119.8 mg/g) and Cu (63.1 mg/g). It exhibited a distinctive selectivity for the removal of metal ions (Cu²⁺ > Zn²⁺ > Cr³⁺ > Pb²⁺ > Cd²⁺) as they coexisted. The influence of initial pH of wastewater for the removal efficiency of metal ions was also investigated and a pH > 7 was preferred.     

Evaluating the photocatalytic activity of Pt/TNT film catalyst

TiO₂ nanotubes (TNT) were prepared by a hydrothermal method from the commercially available TiO₂-P25. Five types of TNT were produced at different temperatures (120 °C, 130 °C, and 150 °C) and by using different reaction times (12 h, 24 h, and 30 h). The photocatalytic reactor that was used is a film catalytic reactor, in which the height of the catalyst is 1.0 mm. The BET and FESEM analysis results showed that TNT130-24 (130 °C, 24 h) and TNT150-12 (150 °C, 12 h) possessed well-formed tubular structures with a high specific surface area (282.9–316.7 m² g⁻¹) and large pore volumes (0.62–0.70 cm³ g⁻¹). However, TNT120-30 (120 °C, 30 h) presented the best photocatalytic activity upon CO removal due to the synergistic effect of TiO₂ nanotubes and TiO₂ particles. After the TNT catalysts were modified with Pt particles, the removal efficiency was in the order of Pt/TNT120-30>Pt/TNT130-24>Pt/P25. Pt/TNT120-30 showed 99% removal efficiency in a continuous photoreactor with a high space velocity of 1.79×10⁴ h⁻¹. The results of the TEM and DRS analyses confirmed that the Pt particles enhanced the photocatalytic reaction, which was attributed to the well-dispersed nature of the 1 nm nanoscaled Pt particles on the surfaces of the TNT catalysts, and narrowed the band gap from 3.22 eV to 3.01 eV.     

Promotional effect of SO2 on the activity of Ir/SiO2 for NO reduction with CO under oxygen-rich conditions

The effect of coexisting SO₂ on the activity of silica-supported noble metal catalysts for the selective reduction of NO with CO in the presence of O₂ was investigated. Pt/SiO₂, Rh/SiO₂, and Pd/SiO₂ showed little catalytic activity for NO reduction, irrespective of coexisting SO₂. Although Ir/SiO₂ showed no NO reduction activity in the absence of SO₂, the presence of SO₂ drastically promoted NO reduction. A comparison of the catalytic performance of Ir/SiO₂ and Ir/Al₂O₃ in the presence of SO₂ showed that Ir supported on SiO₂ is more active than Ir on Al₂O₃. SiO₂ was found to be a more effective support than Al₂O₃. The most outstanding feature of the reaction on the Ir/SiO₂ catalyst was that the coexistence of SO₂ and O₂ is essential for NO reduction to occur. The role of coexisting SO₂ was considered to be not only to stabilize but also to create Ir⁰ sites in an oxidizing atmosphere. FT-IR measurements suggested that a cis-type coordinated species of NO and CO on one iridium atom (

) was an intermediate for NO reduction by CO. Although the

species completely disappeared with the addition of O₂ to the reaction gas, the presence of coexisting SO₂ caused a reappearance of the

species. A reaction mechanism in which N₂ and N₂O are produced via the recombination of dissociated N atoms (N_(a) + N_(a) → N₂) and the formation of dimer (NO)₂-type species (2NO → (NO)_2(a) → N₂O + O_(a)), respectively, is proposed.     

Reactivity of cyrhetrenylphosphines: Synthesis and characterization of oxides,boranes and selenides

Reaction of cyrhetrenylphosphines, of general formula (η⁵-C₅H₄PR₂)Re(CO)₂L (R = Ph, L = CO (1); R = Cy; L = CO (2); R = Ph, L = PMe₃ (3) and R = Ph, L = P(OMe)₃ (4)), with H₂O₂, BH₃·THF or selenium gives the respective cyrhetrenylphosphine oxides, boranes and selenides. These species were characterized by standard spectroscopic techniques (FT-IR, ¹H and ³¹PNMR). Based on the ³¹P⁷⁷Se coupling constant (¹J_P-Se) of the phosphine-selenides, we established the following order of basicity of the parent cyrhetrenylphosphine 2 > 3 > 4 > 1. We also confirmed the opposite electronic effects of the cyrhetrenyl and ferrocenyl groups attached to a –PR₂ unit. Finally, phosphine selenides 2c and 4c were structurally characterized by X-ray diffraction.     

Anodic oxidation of isothiazolin-3-ones in aqueous medium by using boron-doped diamond electrode

Electrochemical degradation of biocide compound, isothiazolin-3-ones, was studied in aqueous medium, with Na₂SO₄ supporting electrolyte using boron-doped diamond (BDD) anode. The redox response of isothiazolin-3-ones at BDD was examined by cyclic voltammetric study. The degradation of isothiazolin-3-ones and its mineralization trend were monitored by UV–vis spectrophotometric method and total organic carbon (TOC) analyzer, respectively. The effect of operating parameters such as applied current density, biocide concentration, electrolyte pH and nature of supporting electrolytes (Na₂SO₄, NaNO₃ and NaCl) on degradation rate was studied in detail. It was established that the hydroxyl radicals (OH) generated at BDD surface were responsible for the degradation and the mineralization of the biocide contaminant. The rate of degradation was almost independent of electrolyte pH but became faster as the applied current density increased and the biocide concentration decreased. The kinetic studies revealed that the biocide decay follows a pseudo-first-order rate. The apparent rate constant for the oxidation of isothiazolin-3-ones was determined to be 2.65 × 10^− 4 s^− 1 at an applied current density of 25 mA cm^− 2 in the presence of 0.1 mol dm^− 3 Na₂SO₄ at pH 6.0. A poor mineralization efficiency was observed in the case of NaCl as supporting electrolyte which cause in-situ generation of chlorine based mediated oxidants such as Cl₂ and OCl⁻ which have negligible influence in mineralizing the isothiazolin-3-ones compared to peroxodisulfate (S₂O₈^2 −) oxidants that formed in the case of Na₂SO₄. The oxidizing ability of the BDD anode was compared with those of Pt and glassy carbon anodes under similar experimental conditions.     

Adsorption of uranyl ions on kaolinite,montmorillonite, humic acid and composite clay material

Adsorption of uranyl ions onto kaolinite, montmorillonite, humic acid and composite clay material (both clays and humic acid) was studied by measuring the system response to clay suspensions (pre-equilibrated with or without uranyl) and to perturbations of the solution chemistry. Adsorption behavior of selected materials under the frame of batch experiments was tested at high uranyl concentrations (6–1170 μg/mL; 2.5 × 10^− 2 to 4.9 μM), whereas that under flow through continuous stirred reactor experiments was tested at low concentrations (1.00 × 10^− 4 to 1.18 × 10^− 4 M). Both experiments were developed at pH 4.5 and ionic strength 0.2 mM. The adsorption experiments follow a Langmuir isotherm model with a good correlation coefficient (R² > 0.97). The calculated amount of adsorbed and desorbed uranyl was carried out by numeric integration of the experimental data, whereas the desorption rates were determined from the breakthrough curve experiments. Kaolinite with highly disordered structure adsorbed less uranyl (3.86 × 10^− 6 mol/g) than well-ordered kaolinite (1.76 × 10^− 5 mol/g). Higher amount of uranyl was adsorbed by montmorillonite (3.60 × 10^− 5 mol/g) and only half of adsorbed amount was desorbed (1.85 × 10^− 5 mol/g). The molecular interactions between kaolinite, montmorillonite, humic acid, composite material and saturated uranyl ion solutions were studied by molecular fluorescence, infrared and X-ray photoelectron spectroscopy. The Stern–Volmer constant obtained for montmorillonite (2.6 × 10³ M^− 1) is higher than for kaolinite (0.3 × 10³ M^− 1). Molecular vibrations of SiO stretching and AlOH bending related to hydroxylated groups (SiOH or AlOH) of kaolinite and montmorillonite show structural changes when uranyl ions are adsorbed. X-ray photoelectron spectroscopy shows that the U 4f_7/2 core level signals occur at 380.5 eV in either kaolinite or montmorillonite that resulted from the interaction of aluminol surface sites with the (UO₂)₃(OH)₅⁺.     

Photodegradation of tetrahalobisphenol-A (X = Cl,Br) flame retardants and delineation of factors affecting the process

The photoassisted degradation (HPLC-UV absorption), dehalogenation (HPLC-IC) and mineralization (TOC decay) of the flame retardants tetrabromobisphenol-A (TBBPA) and tetrachlorobisphenol-A (TCBPA) were examined in UV-irradiated alkaline aqueous TiO₂ dispersions (pH 12), and for comparison the parent bisphenol-A (BPA, an endocrine disruptor) in pH 4–12 aqueous media to assess which factor impact most on the photodegradative process. Complete degradation (2.7–2.8 × 10⁻² min⁻¹) and dehalogenation (1.8 × 10⁻² min⁻¹) of TBBPA and TCBPA occurred within 2 h of UV irradiation, whereas only 45–60% mineralization (2.3–2.7 × 10⁻³ min⁻¹) was complete within 5 h for the flame retardants at pH 12 and ca. 80% for the parent BPA. Factors examined in the pH range 4–12 that impact the degradation of BPA were the point of zero charge of TiO₂ particles (pH_pzc; electrophoretic method), particle or aggregate sizes of TiO₂ (light scattering), and the relative number of OH radicals (as DMPO–OH adducts; ESR spectroscopy) produced in the UV-irradiated dispersion. Dynamics of BPA degradation (2.0–2.4 × 10⁻² min⁻¹) were pH-independent and independent of particle/aggregate size, but did correlate with the number of OH radicals, at least at pHs 4 to 8–9, after which the rates decreased somewhat at pH > 9 with decreasing adsorption owing to Coulombic repulsive forces between the very negative TiO₂ surface and the anionic forms of BPA (pK_as ca. 9.6–11.3), even though the number of OH radicals continued to increase at the higher pHs.     

Optimization of desulphurization of Artvin–Yusufeli lignite with acidic hydrogen peroxide solutions

In this study in which the Taguchi method was used, the optimization of sulphur removal by H₂O₂/H₂SO₄ solutions was carried out over lignite with higher content of sulphur from Artvin/Yusufeli, Turkey. In experiments, the ranges of experimental parameters were between 0.25 and 6.0 mol L⁻¹ for H₂O₂ concentration, 0.25–4 mol L⁻¹ for H₂SO₄ concentration, 10–60 °C for reaction temperature, 0.01–0.08 g mL⁻¹ for solid-to-liquid ratio, 15–120 min for reaction time, 200–300 rpm for stirring speed and 710–120 μm for particle size. The optimum conditions for these parameters have found to be 60 °C of temperature, 0.06 g mL⁻¹ of solid-to-liquid ratio, 60 min of reaction time, 250 rpm of stirring speed and −250 + 180 μm of particle size.A statistical experimental arrangement, L₂₅(5⁶) was prepared to determine optimum sulphur removal and ash removal ratios. The obtained yields were 97.85% in removal of total sulphur, 56.54% in removal of pyritic sulphur, 21.33% in removal of organic sulphur and 61.52% in removal of ash. According to variance analysis, it was seen that all parameters were effective in removal of pyritic and total sulphur, reaction temperature, solid-to-liquid ratio, reaction time, stirring speed, H₂O₂ and H₂SO₄ concentrations in removal of organic sulphur, and other parameters except acid concentration in removal of ash.     

Catalytic conversion of CO,NO and SO2 on the supported sulfide catalyst: I. Catalytic reduction of SO2 by CO

Catalytic reduction of SO₂ to elemental sulfur by CO has been systematically investigated over γ-Al₂O₃-supported sulfide catalysts of transition metals including Co, Mo, Fe, CoMo and FeMo with different loadings of the metals. The sulfided CoMo/Al₂O₃ exhibited outstanding activity: a complete conversion of SO₂ was achieved at a temperature of 300°C. The reaction proceeds catalytically and consistently over time and most efficiently at a molar feed ratio CO/SO₂ = 2. A precursor CoMo/Al₂O₃ oxide which experienced sulfurization through the CO–SO₂ reaction yielded a working sulfide catalyst having a yet lower activity than the CoMo catalyst sulfided before reaction (pre-sulfiding). The catalytic activity of various metal sulfides decreased in order of 4% Co 16% Mo > 4% Fe15% Mo > 16% Mo ≥ 25% Mo > 14% Co ≥ 4% Co > 4% Fe. A DRIFT study showed that CO adsorbs exclusively on CoMo phase and that SO₂ predominantly on γ-Al₂O₃. It is suggested that the Co–Mo–S structure is more adequate than the other metal-sulfur structures for the formation of a carbonyl sulfide (COS) intermediate because of the proper strength of metal–sulfur bond, and catalytically works with γ-Al₂O₃ for the COS–SO₂ reaction.     

Removal of pharmaceutical and personal care products (PPCPs) pollutants from water by novel TiO2–Coconut Shell Powder (TCNSP) composite

Photocatlytic removal of three pharmaceutical and personal care products pollutants using novel TiO₂–Coconut Shell Powder (TCNSP) composite was investigated. The photocatalytic degradation rate of PPCPs generally increased with increasing light intensity and dissolved oxygen concentration. The degradation rate decreased with increasing initial concentration of PPCPs. The PPCPs concentration decreased substantially under irradiation of UVC when used in conjunction with the TCNSP composite. A number of composite/radiation types and intensities were tested. The concentration rate decrease trend was as: UVC/TCNSP > UVA/TCNSP > UVC > UVA. Under the UVC/TCNP combination, 99% removal was achieved compared to 30% for TiO₂.     

A fluorescein derivative FLTC as a chemosensor for Hg2 + and Ag+ and its application in living-cell imaging

FLTC was synthesized and used as a fluorescent chemosensor to detect Hg^2 +. It showed high selectivity toward Hg^2 + over many heavy metal ions in an ethanol–H₂O (3:2, v/v, HEPES buffer, 0.5 mM, pH 7.15) solution with a detection limit of 0.21 μM. After complexation with Hg^2 +, FLTC showed extremely high selectivity toward Ag⁺ with a detection limit of 0.009 μM. Therefore, detection of Hg^2 + and Ag⁺ could be realized using FLTC and the FLTC–Hg^2 + complex, respectively. Cytotoxicity assays and fluorescence microscopy analysis showed that FLTC could be used as a fluorescent probe to detect Hg^2 + and Ag⁺ in L-02 human liver cells.     

UV/S2O82− process for degrading polyvinyl alcohol in aqueous solutions

This investigation evaluates the effectiveness of the UV/S₂O₈²⁻ process in the degradation of polyvinyl alcohol (PVA) in aqueous solutions without adjusting their pH. The effects of UV wavelength and Na₂S₂O₈ dosage on the efficiency of degradation of PVA were examined. The efficiency of degradation of PVA under UV-254 nm exceeded that under UV-365 nm. A larger Na₂S₂O₈ dosage was associated with a higher efficiency of degradation of PVA under UV-254 nm irradiation. However, an excessive Na₂S₂O₈ dosage inhibited the degradation of PVA by the UV-365 nm/S₂O₈²⁻ process. Both UV-254 nm/S₂O₈²⁻ and UV-365 nm/S₂O₈²⁻ processes exhibited pseudo-first-order kinetics. SO₄⁻ was detected by performing quenching studies using specific alcohols, revealing that SO₄⁻ was found to be the predominant radical in the UV-254 nm/S₂O₈²⁻ process. Additionally, the presence of inorganic anions with various effects inhibited the degradation of PVA by the UV-254 nm/S₂O₈²⁻ process. Complete degradation of PVA (20 mg/L) was achieved within 5 min under UV-254 nm using an Na₂S₂O₈ dosage of 0.12 g/L in the absence of inorganic anions, indicating that UV irradiation to activate S₂O₈²⁻ promotes the degradation of PVA in aqueous solutions without adjusting their pH.     

Development of iron-based sorbents for Hg0 removal from coal derived fuel gas: Effect of hydrogen chloride

Laboratory studies were conducted to develop an elemental mercury (Hg⁰) removal process based on the reaction of H₂S and Hg⁰ using iron-based sorbents for coal derived fuel gas. It is well known that hydrogen chloride (HCl) is present in fuel gases derived from some types of coal, but the effect of HCl on the Hg⁰ removal performance of iron-based sorbents in coal derived fuel gas is not yet well understood. In this study, the effects of HCl on the removal of Hg⁰ from coal derived fuel gases over iron-based sorbents such as iron oxide (Fe₂O₃), supported iron oxides on TiO₂, iron oxide–Ca(OH)₂, and iron sulfides were investigated. The Hg⁰ removal experiments were carried out in a laboratory-scale fixed-bed reactor at 80 °C using simulated fuel gas. In the case of iron oxide (Fe₂O₃), the presence of HCl suppressed the Hg⁰ removal rate. In the case of Fe₂O₃ (2 or 5 wt%)/TiO₂, the presence of HCl did not suppress the Hg⁰ removal rate and the activity was stable. The Hg⁰ removal performance of reagent FeS₂ was higher than that of the iron oxide, and not affected by the presence of HCl. The Hg⁰ removal rate of iron oxide–Ca(OH)₂ was not effected by the presence of HCl, because HCl was captured by Ca(OH)₂. The reagent FeS₂ showed higher Hg⁰ removal activity than that of FeS₂ ore. However, the Hg⁰ removal performance of ground and kneaded FeS₂ ore was comparable to that of reagent FeS₂ probably due to the increase in porosity of the FeS₂ ore by grinding and kneading.     

Mercury(II) removal from aqueous solution by sorption onto alginate,pectate and polygalacturonate calcium gel beads. A kinetic and speciation based equilibrium study

Gel beads of calcium alginate, pectate and polygalacturonate salts have been tested as sorbent materials for mercury(II) removal from aqueous solutions. Physico-chemical properties of gel beads, defined by SEM–EDX, TGA and texture and density analysis, were correlated with gel beads sorption capacity towards Hg²⁺ ion. A speciation study in aqueous solution was carried out to define the strength of interaction of mercury ion with the polymers investigated and to assess the more suitable experimental conditions to achieve the best effectiveness of Hg²⁺ sorption by gel beads. On the basis of the speciation study, pH values in the 3–5.5 pH range were considered appropriated for mercury(II) sorption by gel beads. Kinetics of mercury(II) sorption and calcium(II) release from the sorbent materials were studied at pH 3, 3.6 and 5.2. The highest sorption rate (K) and amount of mercury(II) adsorbed were obtained at pH 3 and 3.6; therefore, pH 3.3 was chosen for the equilibrium study of Hg²⁺ sorption at 25 °C. The results obtained by using Langmuir and Freundlich isotherm equations show the following sorption capacity trend: Ca–Pect > Ca–PGA > Ca–AA.