Highly Efficient Dye Removal from Aqueous Solutions Using Simple Chemical Modification of Wood Sawdust

Abstract

This study examined the efficiency of oxidized wood meal for removal of methylene blue (MB) as a typical basic dye from aqueous waste streams. The adsorption process was performed using sawdust treated with KMnO₄, K₂Cr₂O₇, and H₂O₂ oxidants. Among the tested chemical oxidants, KMnO₄ was found to be more effective for modification of sawdust for dye uptake. Based on the breakthrough analysis, the highest column capacity of 227 mg g^?1 was obtained for the KMnO₄/SD. Sorption capacity of KMnO₄ treated sawdust for dye uptake was about seven times that of untreated sawdust (SD). The nature and morphology of adsorbents were characterized by SEM, XRD, and FTIR analysis. The adsorption behavior of KMnO₄/SD was found to be a strongly pH-dependent process and the maximum adsorption efficiency was obtained at pH 10. Dye-loaded KMnO₄/SD sorbent can be regenerated using low-cost chemicals.     

Surface and structural characterization of multi-walled carbon nanotubes following different oxidative treatments

Six commonly used wet chemical oxidants (HNO₃, KMnO₄, H₂SO₄/HNO₃, (NH₄)₂S₂O₈, H₂O₂, and O₃) were evaluated in terms of their effects on the surface chemistry and structure of MWCNTs using a combination of analytical techniques. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDX) were used to characterize the extent of surface oxidation, while chemical derivatization techniques used in conjunction with XPS allowed the concentration of carboxyl, carbonyl, and hydroxyl groups at the surface to be quantified for each MWCNT sample. Our results indicate that the distribution of oxygen-containing functional groups was insensitive to the reaction conditions (e.g., w/w% of oxidant), but was sensitive to the identity of the oxidant. MWCNTs treated with (NH₄)₂S₂O₈, H₂O₂, and O₃ yielded higher concentrations of carbonyl and hydroxyl functional groups, while more aggressive oxidants (e.g., HNO₃, KMnO₄) formed higher fractional concentrations of carboxyl groups. IR spectroscopy was unable to identify oxygen-containing functional groups present on MWCNTs, while Raman spectra highlighted the frequently ambiguous nature of this technique for measuring CNT structural integrity. TEM was able to provide detailed structural information on oxidized MWCNT, including the extent of sidewall damage for different oxidative treatments.     

Graft copolymerization of polyfurfuryl alcohol and cellulose

Viscosity of polyfurfuryl alcohol (PFA) and addition of hydroquinone exert a strong positive effect on grafting polyfurfuryl alcohol to cellulose fiber with H₂O₂/Fe²⁺ oxidant in an aqueous slurry at pH 2. Composition of the atmosphere and the nature of acids used to adjust pH does not influence the reaction, with the exception of phosphoric acid, which negatively influences polymer loading. Conducting the reaction in nonaqueous media inhibits grafting. K₂S₂O₈, Ce(SO₄)₂, and K₂Cr₂O₇ perform as well as H₂O₂/Fe²⁺, whereas H₂O₂/thiourea dioxide, H₂O₂/thiourea, NH₄VO₃, KMnO₄, and KNO₃ give inferior polymer loads; Mn³⁺/acetylacetonate and azobisisobutyronitrile are ineffective. A small improvement in polymer loading is obtained by gradual addition of the oxidant to the reaction slurry.     

Anodic behaviour of titanium in concentrated sulphuric acid solutions. Influence of some oxidizing inhibitors

The anodic polarisation behaviour of the titanium electrode and the rate of corrosion are measured in aqueous sulphuric acid solutions as a function of the electrolyte concentration. Increasing acid concentration increases the critical current for passivity. This current passes through a maximum (4.88 mA cm^–2) at 25 N and then decreases again. Increasing temperature increases the critical current for passivity. The effect of oxidizing agents such as K₂Cr₂O₇, KMnO₄, KIO₃, Na₂MoO₄, NaClO₃, HNO₃ and TiCl₄ on the polarisation of titanium are also investigated. K₂Cr₂O₇, HNO₃, TiCl₄ are the most powerful corrosion inhibitors at room temperature and also at 80° C in 10 N H₂SO₄, while in more concentrated sulphuric acid solution (25 N), corrosion inhibition is observed only by HNO₃ for a very short period.     

The synergetic depression effect of KMnO4 and CMC on the depression of galena flotation

The mechanism of carboxymethyl cellulose (CMC) on the galena surface and the enhancement of KMnO₄ on the depression of CMC to galena were investigated by flotation test, surface adsorption experiments, scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). Flotation test results indicated that the addition of KMnO₄ under alkaline condition significantly enhanced the depression effect of CMC on galena. Surface adsorption experiments of butyl xanthate (BX) and CMC demonstrated that the adsorption amount of BX decreased after CMC was added into the pulp. And the adsorption amount of CMC increased while BX decreased sharply when KMnO₄ was added into the pulp. After galena was treated with KMnO₄ and CMC, dim spots (oxidation sites) on the surface of galena were observed by SEM-EDS. Results showed the high contents of C and O on the oxidation sites. XPS results indicated that oxidation-reduction reaction occurred on the mineral surface, and PbS₂O₃ or Pb(OH)₂ was probably the main component of the oxidization sites. The CMC could be adsorbed on the oxidation sites by the hydrogen bond to form a hydrophilic membrane on the mineral surface lead to galena depression. All results showed that KMnO₄ could enhance the depression effect of CMC on galena.     

Role of Support and Promoter in the Selective Conversion of Isophorone to 3,5-Xylenol over Chromia Catalysts

A detailed study has been undertaken regarding the role of support and promoter towards 3,5-xylenol selectivity improvements in the vapor-phase aromatization of isophorone. The supports used in this study include A1₂O₃, SiO₂, ZrO₂, MgO and carbon-covered alumina for Cr₂O₃ catalysts. K₂O has been used as a promoter for these catalysts. Influence of solvent during Cr₂O₃/MgO catalyst preparation step has also been studied. The parameters governing the aromatization selectivity observed from this study are: moderate acidic sites, coordinatively unsaturated sites of Cr₂O₃ and smaller crystallites of Cr₂O₃.     

SHS-produced β-sialons as supports for oxidation catalysts

SHS-produced β-sialons Si_6−z Al _z O _z N_8−z (z = 1, 3, 4) were tested as supports for oxidation catalysts comprising of unary, binary or ternary mixtures of transition metal (Cr, Mn, Fe, Co, Ni, Cu) oxides and also KMnO₄ and K₂Cr₂O₇. In oxidation of CO and propane (C₃H₈), the highest activity was exhibited by the catalysts based on cobalt oxides. Suggested are some methods for activation of the above catalysts.      

烟气气相组分及Ca（OH）2对KMnO4氧化NO的影响机理

在固定床反应器中考察了KMnO₄氧化烟气中NO的过程,分析了烟气组分H₂O、O₂及SO₂对NO氧化过程的影响规律,得到了Ca（OH）₂对KMnO₄氧化NO的影响机理。实验结果表明,H₂O是KMnO₄氧化NO的必要条件;在含H₂O条件下,O₂可以提高NO氧化率。SO₂与氧化剂反应生成无水钾镁钒类复盐K₂Mn₂（SO₄）₃对NO氧化具有负面作用;Ca（OH）₂的加入提高了氧化剂表面的固体碱度从而促进氧化过程进行;通过添加Ca（OH）₂可以降低SO₂对NO氧化过程的负面影响。根据气体成分和产物分析可知,KMnO₄在钙基吸收剂表面氧化烟气中NO的机理可能是KMnO₄以离子态将吸附在氧化剂表面的NO和SO₂氧化为NO₂和SO₃,生成的NO₂、SO₃再传递到氧化位临近的碱性位被吸收。     

A novel approach to mesoporous anatase TiO2: Oxidation of TiC by nitric acid

TiO₂ has been prepared by a novel, mild one-step reaction between TiC and aqueous HNO₃ at 70 °C. This material possesses an anatase crystal form and a narrow pore-size distribution of mesoporous channels. The BET surface area, average pore diameter, and total pore volume are 332.7 m²/g, 3.28 nm, and 0.23 cm³/g, respectively. Our method is a template-free synthesis process, distinct from sol–gel methods for mesoporous TiO₂ fabrication using structure-directing surfactants or polymers. TiO₂ is not generated from TiC reacting with other acids and oxidants, such as HCl, H₂SO₄, H₃PO₄, KMnO₄, K₂Cr₂O₇, Na₂S₂O₇, H₂O₂, and Na₂CrO₄, at a similar reaction condition. Since the average particle size of the mesoporous TiO₂ produced is much larger than that of the TiC starting material, the mechanism for the formation of the mesoporous TiO₂ is not via mesopore-etching of TiC particles and transformation of TiC pore walls into TiO₂ by HNO₃. It is likely that TiC is first transformed into Ti_mX_n species, followed by hydrolysis to form mesoporous TiO₂.     

Model study of pyrite demineralization by hydrogen peroxide oxidation at 30 °C in the presence of metal ions (Ni2+, Co2+ and Sn2+)

Dissolution of pyrite involving oxidation by hydrogen peroxide (H₂O₂) in the presence of metal ions (Ni²⁺, Co²⁺ and Sn²⁺) has been investigated. Before oxidation, pure and well crystalline structure of the acid washed pyrite sample, used in the present investigation, was confirmed by X-ray diffraction and chemical analysis. Oxidation of pyrite was examined by the determination of soluble sulfur. The rate of oxidation of pyrite with H₂O₂ is best represented by determining the rates of total soluble sulfur production. Each experiment was carried out for short (1–4 h) and extended (24 h) time periods. Pyrite is oxidized by H₂O₂ (1:1) up to the extent of 31.3% at short time period, which however remained the same even at extended time period. Increased amount of soluble sulfur has been observed when pyrite was oxidized by H₂O₂ (1:1) in the presence of Ni²⁺ or Co²⁺ or Sn²⁺ ion at short time period. The effectiveness of these metal ions in relation to pyrite oxidation at short time period decreases in the order Co²⁺>Sn²⁺>Ni²⁺, while at extended time period the order is Co²⁺>Ni²⁺>Sn²⁺. With Co²⁺ ion, the highest pyrite oxidation is obtained both at short (34.0%) and extended (35.0%) time period, while it is the lowest 31.3% with Ni²⁺ ion at short time and 25.3% with Sn²⁺ ion at extended time period. The effect of chloride ion on the rate of oxidation of pyrite is not pronounced in the metal ion containing systems. Substantial depletion in the concentration of externally added metal ions is in good agreement with the level of oxidation and infers certain adsorption or precipitation of metal ions on pyrite surface. The results of this study throw a new light of the influence of metal ions in the dissolution of pyrite in oxidation systems and has considerable applications in fields of demineralization, desulfurization and environmental science.     

Oxidative dissolution of pyrite in acidic media

The pyrite oxidative dissolution in air-saturated (AS), H₂O₂, and Fe³⁺ solutions at pH 2.5 and 25 °C was investigated by electrochemical and aqueous batch experiments. The corrosion current density (i _corr) increases from AS solution to Fe³⁺ and H₂O₂ solutions. For the same oxidant, i _corr increases when the concentration of the oxidant increases. Similar variation was observed for the corrosion potential (E _corr). Electrochemical impedance spectroscopy measurements have indicated that in AS and H₂O₂ solutions, the charge transfer is the rate determining step of pyrite oxidative dissolution. In the presence of Fe _(aq) ³⁺ , both the charge transfer process and mass transfer caused by the diffusion of oxidant or reaction products across the interface of electrode control the mineral oxidative dissolution. The corrosion current densities of oxidative dissolution measured by electrochemical methods are higher than those estimated from dissolution rates determined by aqueous bath experiments. The observed differences suggest that the mechanism of polarized electrode oxidation is different by the mechanism of pyrite oxidation under open circuit conditions.     

毒砂型高砷金精矿的细菌氧化

通过毒砂型高砷金精矿和单矿物纯毒砂的氧化对比摇瓶试验,发现由于金精矿中黄铁矿的存在促进了矿物的脱砷效率,脱砷速度明显高于纯毒砂。经过10 d和15 d的细菌氧化脱砷,金精矿和毒砂的最终脱砷率分别达到93.90%和64.45%。对毒砂氧化渣的显微镜观察以及XRD衍射分析发现,毒砂颗粒外壁被氧化过程中产生的黄氨铁矾沉淀所覆盖,隔绝了它与外界环境的接触,最终导致了毒砂氧化速度缓慢,脱砷效果不够彻底。     

Adsorption of cadmium(II) from aqueous solution by surface oxidized carbon nanotubes

Carbon nanotubes (CNTs) were oxidized with H₂O₂, KMnO₄ and HNO₃. Their physicochemical properties were investigated by BET N₂ adsorption, laser particle examination, Boehm’s titration, zeta potential measurement and cadmium(II) adsorption. The experimental results suggest that cadmium(II) adsorption capacities for three kinds of oxidized CNTs increase due to the functional groups introduced by oxidation compared with the as-grown CNTs. The cadmium(II) adsorption capacity of the as-grown CNTs is only 1.1 mg g⁻¹, while it reaches 2.6, 5.1 and 11.0 mg g⁻¹ for the H₂O₂, HNO₃ and KMnO₄ oxidized CNTs, respectively, at the cadmium(II) equilibrium concentration of 4 mg l⁻¹. Adsorption of cadmium(II) by CNTs was strongly pH-dependent and the increase of adsorption capacities for HNO₃ and KMnO₄ oxidized CNTs is more obvious than that of the as-grown and H₂O₂ oxidized CNTs at lower pH regions. The experiments of CNT dosage effect on the cadmium(II) adsorption show that the adsorption capacity for KMnO₄ oxidized CNTs has a sharper increase at the CNT dosage from 0.03 to 0.08 g per 100 ml than the as-grown, H₂O₂ and HNO₃ oxidized CNTs and its removal efficiency almost reaches 100% at CNT dosage of 0.08 g per 100 ml. Analysis revealed that the KMnO₄ oxidized CNTs hosted manganese residuals, and these surely contributed to cadmium sorption to a yet-undefined extent.     

Some aspects of the electrochemistry of the flotation of pyrrhotite

The iron sulfide mineral, pyrrhotite (Fe_(1–x)S), has long been known to be more difficult to recover by flotation from alkaline slurries than many other base metal sulfide minerals. This paper summarizes the results of an electrochemical study of the surface reactions that occur during the flotation of nickeliferous pyrrhotite in the recovery of nickel and the platinum group metals. Mixed potential measurements conducted with natural pyrrhotite electrodes in various stages of an operating flotation plant showed that the mineral potential is positive to the equilibrium potential of the xanthate/dixanthogen couple. Similar results were obtained during batch flotation experiments and in synthetic solutions in the laboratory. Cyclic voltammetric and potentiostatic current/time transient experiments were used to investigate the oxidation of pyrrhotite under various conditions. In addition, the reduction of oxygen, the reaction of copper ions and the oxidation of xanthate ions at the mineral surface were investigated. The formation of dixanthogen on pyrrhotite surfaces is thermodynamically favourable in plant flotation slurries. However the interaction with xanthate at pH values above 7 is inhibited by a surface species formed during the conditioning prior to xanthate addition. In acidic solutions copper ions react readily with pyrrhotite to form a species, possibly CuS that can be oxidized at potentials above 0.4 V. At pH 9 this species does not form and there is no electrochemical reaction between pyrrhotite and copper ions. The beneficial effects of copper ions to flotation performance appear to be related to an enhancement of the oxidation of xanthate.     

Selective etching of CoFeNiCu/Cu multilayers

Selective etching of CoFeNiCu/Cu multilayers was investigated with different solutions: HNO₃/alcohol, FeCl₃/HCl, K₂Cr₂O₇/H₂SO₄ and dilutions of FeCl₃/HCl, K₂Cr₂O₇/H₂SO₄. Polarization curves on a rotating disk electrode were used to assess the corrosion potential and current density of Cu, and Co-rich alloys. Preferential etching of the Co-rich alloy was attributed to either a less positive corrosion potential or a higher corrosion current density compared to the Cu layer. A dilution of the aqueous K₂Cr₂O₇/H₂SO₄ solution was considered most promising for submicron structure development. ¹ISE member.     

Suppression of floatability of pyrite in coal processing by carrier microencapsulation

Carrier microencapsulation, CME, is a technique to form a thin layer of metal oxide or hydroxide on pyrite surface using a water soluble organic carrier combined with metal ions. The present study investigated the effect of CME using a tris-catecholato complex of Si⁴⁺, Si(cat)₃²⁻ on pyrite-coal separation by dynamic bubble pick-up experiments and Hallimond tube flotation experiments using coal, pyrite, and a coal-pyrite mixture. The mineral samples were treated in 0-5 mol m^− 3 Si(cat)₃²⁻ solutions at pH 4-9 at treatment times of 1-24 h. Dynamic bubble pick-up experiments showed that CME treatment converted the pyrite surface from hydrophobic to hydrophilic but did not affect coal's hydrophobic surface. The results of the Hallimond tube flotation experiments of a coal-pyrite mixture at pH 7-9 in the presence of kerosene as a collector showed that pyrite floatability was selectively suppressed after 1 h CME treatment with 0.5 mol^− 3 Si(cat)₃²⁻ while both coal and pyrite were floated without the treatment. This indicates that CME treatment is effective in suppressing pyrite floatability in coal-pyrite flotation.     

The Catalytic Baeyer–Villiger Oxidation of Cyclohexanone to ε-Caprolactone over Stibium-containing Hydrotalcite

A series of hydrotalcite-like compounds were prepared under microwave irradiation, which were used to catalyze the Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone with hydrogen peroxide as oxidant. The results show that stibium-containing hydrotalcite (Sb-HTL) has good catalytic properties in the reaction. In the Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone with H₂O₂ catalyzed by Sb-HTL, the effects of reaction time, reaction temperature, amount of catalyst and H₂O₂/cyclohexanone molar ratio are also investigated in details. It is shown the cyclohexanone conversion and ε-caprolactone selectivity can reach 79.15 and 93.84%, respectively, under the optimum reaction conditions. Furthermore, Sb-HTL can be reused for six times without obvious loss of activity and selectivity. Therefore, Sb-HTL is reusable and would be a promising catalyst for the Baeyer–Villiger oxidation using green and cheap oxidants like hydrogen peroxide instead of peroxycarboxylic acids.     

Fabrication of mesoporous Cr2O3 with highly distributed α-Fe2O3 and Pt nanoparticles for ultrafast H2 evolution rate

In the present contribution, p-n type heterojunction α-Fe₂O₃/Cr₂O₃ S-scheme system photocatalyst has been fabricated utilizing a sol-gel approach with assisted nonionic surfactant for a highly effective H₂ evolution rate under visible illumination. Pt NPs have been reduced by photodeposition during the photocatalytic reaction to collect Pt@α-Fe2O3/Cr2O3 finally. XRD analysis of Fe₂O₃/Cr₂O₃ nanocomposites verified the construction of Fe₂O₃ and Cr₂O₃ with rhombohedral phases. TEM images of Cr₂O₃ NPs were almost spherical and uniform in shape and size (20 ± 5 nm), and very small Fe₂O₃ NPs (3-5 nm) were distributed on the mesoporous Cr₂O₃ networks. The obtained α-Fe₂O₃/Cr₂O₃ photocatalyst exhibited noteworthy photocatalytic H₂ evolution with high efficiency and stability for 45 h. Interestingly, the photocatalytic H₂ evolution rate gradually boosted with the extent of Fe₂O₃ percentage up to 15% and its rate of 2215.4 μmol g^-1h^-1, which was fostered 7.25 folds larger than that of Cr₂O₃ NPs (305.7 μmol g^-1h^-1). The enhancement H₂ evolution rate of Fe₂O₃/Cr₂O₃ photocatalyst in comparison with bare Cr₂O₃ NPs was ascribed to facilitate the separation of photocarriers and existing considerable reactive sites. In addition, constructing n-type Fe₂O₃ and p-type Cr₂O₃ with close contact is essential in improving the H₂ evolution rate. The possible photocatalytic mechanism over Fe₂O₃/Cr₂O₃ nanocomposite was addressed based on electrochemical measurements. The construction of the S-scheme system of Fe₂O₃/Cr₂O₃ nanocomposite could be suggested to improve the separation of photocarriers through optimal transfer channels owing to the formation of synergistic characteristics. Our results provide avenues for constructing stable photocatalysts with high efficiency for H₂ evolution through visible exposure.     

Partial oxidation of alkenes by a membrane catalyst conducting H+ and e−

Partial oxidation of C₂H₄ to MeCHO (>95% selectivity) with O₂ by a new type of membrane catalyst was studied at 353 K. Reaction system was (C₂H₄, H₂O | membrane catalyst | O₂, NO). The membrane catalyst was assembled from three sheets, porous catalyst for oxidation of C₂H₄, mixed conductor of H⁺ and e⁻, porous catalyst for the reduction of O₂. NO functioned as a co-catalyst for reduction of O₂ to H₂O. This three-layered membrane catalyst functioned as a hydrogen permeation membrane.