Contaminants In Aqueous Solution Research Articles

Studies on Synthesis, Characterization, and Adsorption of Cationic Dyes from Aqueous Solutions Using Magnetic Composite Material from Natural Clay in Central Kalimantan, Indonesia

Clay is a natural material from crystalline silicate with layered structures, has high cation exchange capacity, and large surface area. These advantages can be used as an adsorbent for the removal of contaminants in aqueous solutions, such as heavy metals and dyes. In Indonesia, clays from Java, Sulawesi, and Sumatra islands have been used as adsorbent, furniture, and construction materials. Due to limited information about basic characteristics of clay from Kalimantan, this clay has not been utilized well. Therefore, natural clay from Kalimantan, especially in Central Kalimantan, was used as adsorbent of cationic dyes in this present study. However, the clay has difficulty for separating the solid phase from aqueous solution after adsorption process. To solve this problem, combining clay with magnetic material was opted. The objectives of this study are to synthesize the magnetic composite material from natural clay by coprecipitation method and to characterize the synthesized magnetic composite material using an x-ray diffraction method, transmission electron microscopy, and vibrating sample magnetometer. The adsorption properties of the synthesized magnetic composite material were evaluated using rhodamine B and methylene blue dyes in aqueous solution. Before magnetic composite material was synthesized, the clay was previously being activated for removing impurities. The magnetic material formed in the structure of clay had magnetite with particle size of 2.75 nm and the magnetization value of 24.91emu/g. The adsorption capacities of natural clay, activated clay, and magnetic composite of clay in rhodamine B were 34.29, 76.27, and 81.46 mg/g, respectively, while in methylene blue were 30.25, 83.92, and 133.90 mg/g, respectively. These results suggested that magnetic composite of clay can increase the adsorption capacities against dyes and accelerate the separation of the adsorbent solid phase from aqueous solution with largest adsorption capacity on methylene blue dye.

Green Synthesis, Characterization and Application of Proanthocyanidins-Functionalized Gold Nanoparticles.

Green synthesis of gold nanoparticles using plant extracts is one of the more promising approaches for obtaining environmentally friendly nanomaterials for biological applications and environmental remediation. In this study, proanthocyanidins-functionalized gold nanoparticles were synthesized via a hydrothermal method. The obtained gold nanoparticles were characterized by ultraviolet and visible spectrophotometry (UV-Vis), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurements. UV-Vis and FTIR results indicated that the obtained products were mainly spherical in shape, and that the phenolic hydroxyl of proanthocyanidins had strong interactions with the gold surface. TEM and XRD determination revealed that the synthesized gold nanoparticles had a highly crystalline structure and good monodispersity. The application of proanthocyanidins-functionalized gold nanoparticles for the removal of dyes and heavy metal ions Ni2+, Cu2+, Cd2+ and Pb2+ in an aqueous solution was investigated. The primary results indicate that proanthocyanidins-functionalized gold nanoparticles had high removal rates for the heavy metal ions and dye, which implies that they have potential applications as a new kind of adsorbent for the removal of contaminants in aqueous solution.

Degradation of organic pollutants by Vacuum-Ultraviolet (VUV): Kinetic model and efficiency

Vacuum-Ultraviolet (VUV), an efficient and green method to produce hydroxyl radical (•OH), is effective in degrading numerous organic contaminants in aqueous solution. Here, we proposed an effective and simple kinetic model to describe the degradation of organic pollutants in VUV system, by taking the •OH scavenging effects of formed organic intermediates as co-existing organic matter in whole. Using benzoic acid (BA) as a •OH probe, •OH was regarded vital for pollutant degradation in VUV system, and the thus developed model successfully predicted its degradation kinetics under different conditions. Effects of typical influencing factors such as BA concentrations and UV intensity were investigated quantitatively by the model. Temperature was found to be an important influencing factor in the VUV system, and the quantum yield of •OH showed a positive linear dependence on temperature. Impacts of humic acid (HA), alkalinity, chloride, and water matrices (realistic waters) on the oxidation efficiency were also examined. BA degradation was significantly inhibited by HA due to its scavenging of •OH, but was influenced much less by the alkalinity and chloride; high oxidation efficiency was still obtained in the realistic water. The degradation kinetics of three other typical micropollutants including bisphenol A (BPA), nitrobenzene (NB) and dimethyl phthalate (DMP), and the mixture of co-existing BA, BPA and DMP were further studied, and the developed model predicted the experimental data well, especially in realistic water. It is expected that this study will provide an effective approach to predict the degradation of organic micropollutants by the promising VUV system, and broaden the application of VUV system in water treatment.

Solar light efficient photocatalytic activity degradation of emergent contaminants by coated TiO2 nanoparticles

The photocatalytic degradation of different emergent contaminants in aqueous solutions has been studied by using oligomer-coated TiO2 nanoparticles under solar light irradiation.

Removal of Typical Organic Contaminants with a Recyclable Calcined Chitosan-Supported Layered Double Hydroxide Adsorbent: Kinetics and Equilibrium Isotherms

In this work, the calcined chitosan (CS)-supported layered double hydroxides were prepared, characterized, and further applied to remove organic contaminants in aqueous solution. The chitosan-supported layered double hydroxide calcined at 400 °C (CSLDO400) was found to be effective for the adsorption of azo dye and antibiotic. CSLDO400 showed excellent adsorption performance at a wide pH range from 5 to 9 for methyl orange (MO) while the adsorption of tetracycline (TC) was most efficient at a pH of 9, and the optimal CSLDO400 dosages were 0.175 g L–1 for MO and 0.375 g L–1 for TC. The divalent and trivalent anions have a great effect on removal efficiency of MO and TC, while the effect of monovalent anions adsorption can be neglected. The adsorption kinetics indicated that the MO and TC removal followed the pseudo-second-order model. In addition, it can be fitted well with both the Langmuir and Freundlich model for MO and TC at 298 K, respectively. The adsorptions of MO and TC on CSLDO400 were both sponta...

Enhanced Solar-Driven Applications of ZnO@Ag Patchy Nanoparticles

ZnO@Ag patchy nanostructures were demonstrated to be efficient and stable photocatalysts for the photodegradation of organic contaminants in aqueous solutions. The photoinduced charge transfer from the conduction band of ZnO toward the Fermi level of the noble metal was favored and exploited to enhance the photocatalytic efficiency of ZnO, with a mechanism based on hole stabilization. Naked ZnO and ZnO@Ag patchy nanostructures were demonstrated to degrade methylene blue, a model compound, in aqueous solution under 370–800 nm light irradiation (100 mW cm–2); in particular, the introduction of silver nanoparticles allowed one to increment twice the constant rate of the reaction when fitted as pseudo-first-order kinetics. Furthermore, the degradation of 2,4-dichlorophenol under direct sunlight irradiation was studied. The photo-oxidation catalyzed by patchy nanostructures was noticeably increased. In fact, the observed half time (t1/2) was reduced by almost 4 times in comparison with the value observed for b...

Application of HDTMA-intercalated bentonites in water waste treatment for U(VI) removal

Bentonite deposits in Slovakia are systematically investigated as potential adsorbents for wastewater and radioactive waste treatment applications. Herein, adsorption properties (isotherms, kinetics and thermodynamics) of raw and organo-modified bentonites towards uranium species in aquaeous solutions were investigated. Organo-modified bentonites was prepared by practical and simple chemical modification method with hexadecyltrimethylammonium bromide (denoted as HDTMA-bentonites). The adsorption processes of U(VI) on HDTMA-bentonites were spontaneous and endothermic, and well simulated by pseudo-second-order model. The maximum adsorption capacity of U(VI) was calculated to be 31.45 mg/g at pH 8.5 and T = 298 K. Slovak bentonites Jelsový potok and Kopernica, their natural and HDTMA-modified forms might be a promising sorbent for the treatment of U(VI) contaminants in aqueous solutions.

Shape-controlled Co 3 O 4 catalysts for advanced oxidation of phenolic contaminants in aqueous solutions

Abstract Three different Co3O4 materials in sphere, cube and truncated cube were prepared by a hydrothermal process and tested in catalytic phenol degradation using oxone®. The properties of the Co3O4 were characterized by several techniques such as X-ray diffraction (XRD), N2 adsorption, and scanning electron microscopy (SEM). Co3O4-cube is highly effective in heterogeneous activation of oxone® to produce sulfate radicals for phenol degradation and the activity of catalysts shows an order of Co3O4-cube > Co3O4-sphere > Co3O4-truncated cube. Kinetic study showed that phenol degradation followed a first order reaction.

Normal and Inverse Diffusive Isotope Fractionation of Deuterated Toluene and Benzene in Aqueous Systems

Diffusive isotope fractionation of organic contaminants in aqueous solution is difficult to quantify, and only a few experimental data sets are available for compounds of environmental interest. In this study, we investigate diffusive fractionation of perdeuterated and nondeuterated benzene and toluene. Multitracer experiments were carried out in 1-D gel dissection tubes and in a quasi-2-D flow-through porous medium. The experiments allowed us to simultaneously and directly compare the diffusive and dispersive behavior of benzene and toluene. We observed an unexpected, opposite behavior of the two monoaromatic hydrocarbons. Toluene showed a normal diffusive isotope effect (DC7D8/DC7H8 = 0.96) with enrichment of the nondeuterated isotopologue in the direction of the diffusive and transverse dispersive fluxes. Conversely, the measured trends for benzene indicate inverse diffusive fractionation (DC6D6/DC6H6 = 1.02), with a remarkably faster diffusion rate of the perdeuterated isotopologue that was enriched i...

Template-free synthesis of N-doped carbon with pillared-layered pores as bifunctional materials for supercapacitor and environmental applications

Cross-linked, N-doped, pillared-layered porous carbons (NCs) were prepared via a one-pot, template-free pyrolysis process at 600 (NC600), 700 (NC700) and 800 °C (NC800), which have bifunctional applications in supercapacitors and environmental remediation. NC700 displays a high surface area (2118 m2 g−1) and a specific capacitance of 305 F g−1 at 0.2 A g−1 in a two-electrode setup. The maximum energy density of NC700 was 20.4 W h/kg at a power density of 139 W kg−1 and 89.1% capacitance was retained after 10000 cycles of charge-discharge at 5 A g−1. For water remediation, NC800 displayed high adsorption capacities towards flame retardant tetrabromobisphenol A (TBBPA, 372 mg g−1) and antibiotic sulfachloropyridazine (SCP, 288 mg g−1) solutions, while NC700 showed the most efficient SCP oxidation removal. These results suggest low-cost and green carbon materials as electrodes in flexible energy storage devices, metal-free adsorbents as well as catalysts for high efficient removal of emerging contaminants in aqueous solution.

Comparison study on photocatalytic oxidation of pharmaceuticals by TiO2-Fe and TiO2-reduced graphene oxide nanocomposites immobilized on optical fibers

Incorporating reduced graphene oxide (rGO) or Fe3+ ions in TiO2 photocatalyst could enhance photocatalytic degradation of organic contaminants in aqueous solutions. This study characterized the photocatalytic activities of TiO2-Fe and TiO2-rGO nanocomposites immobilized on optical fibers synthesized by polymer assisted hydrothermal deposition method. The photocatalysts presented a mixture phase of anatase and rutile in the TiO2-rGO and TiO2-Fe nanocomposites. Doping Fe into TiO2 particles (2.40eV) could reduce more band gap energy than incorporating rGO (2.85eV), thereby enhancing utilization efficiency of visible light. Incorporating Fe and rGO in TiO2 decreased significantly the intensity of TiO2 photoluminescence signals and enhanced the separation rate of photo-induced charge carriers. Photocatalytic performance of the synthesized nanocomposites was measured by the degradation of three pharmaceuticals under UV and visible light irradiation, including carbamazepine, ibuprofen, and sulfamethoxazole. TiO2-rGO exhibited higher photocatalytic activity for the degradation of pharmaceuticals under UV irradiation, while TiO2-Fe demonstrated more suitable for visible light oxidation. The results suggested that the enhanced photocatalytic performance of TiO2-rGO could be attributed to reduced recombination rate of photoexcited electrons-hole pairs, but for TiO2-Fe nanocomposite, narrower band gap would contribute to increased photocatalytic activity.

Uranium biosorption from aqueous solution by the submerged aquatic plant Hydrilla verticillata.

The biosorption characteristics of U(VI) from aqueous solution onto a nonliving aquatic macrophyte, Hydrilla verticillata (dry powder), were investigated under various experimental conditions by using batch methods. Results showed that the adsorption reached equilibrium within 60 min and the experimental data were well fitted by the pseudo-first-order kinetic model. U(VI) adsorption was strongly pH dependent, and the optimum pH for U(VI) removal was 5.5. Isotherm adsorption data displayed good correlation with the Langmuir model, with a maximum monolayer adsorption capacity of 171.52 mg/g. Thermodynamic studies suggested that U(VI) adsorption onto H. verticillata was an exothermic and spontaneous process in nature. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that the amino and hydroxyl groups on the algal surface played an important role in U(VI) adsorption. The mechanisms responsible for U(VI) adsorption could involve electrostatic attraction and ion exchange. In conclusion, H. verticillata biomass showed good potential as an adsorption material for the removal of uranium contaminants in aqueous solution.

Zeolitic imidazolate framework-67 (ZIF-67) rhombic dodecahedrons as full-spectrum light harvesting photocatalyst for environmental remediation

The inferior utilization efficiency of light is the main obstacle to the practical application of traditional photocatalysts such as TiO2 and ZnO. In this regard, the development of novel photocatalysts with the capability of harvesting full spectrum light (from ultraviolet (UV) to near-infrared (NIR)) energy is a promising solution for solar energy conversion and environmental remediation. Here, we report the discovery of a single material that can harvest UV, visible (VIS), and NIR radiations to decompose heavy metal contaminants in aqueous solution. Zeolitic imidazolate framework-67 (ZIF-67) rhombic dodecahedrons were synthesized through a facile solution approach and employed in the reduction of Cr(VI) under UV−VIS−NIR pulsed laser irradiation, which was generated from the fundamental, second and third harmonics of Nd:YAG laser, respectively. The nanostructures showed efficient Cr(VI) reduction under UV, VIS and NIR laser irradiation and the measured reduction efficiency (%) was 71.22%, 69.52%, and 40.79%, respectively after 120 min. A possible explanation for the photocatalytic activity in Cr(VI) reduction was proposed. This is the first study of its kind where pulsed laser and ZIF-67 rhombic dodecahedrons capable of harvesting full spectrum light energy have been employed for the removal of Cr(VI) from water. The extraordinary capacity of harvesting full-spectrum light and long-term stability make ZIF-67 a potential photocatalyst for environmental remediation.

Fabrication of ZnO-ZnS@polyaniline nanohybrid for enhanced photocatalytic degradation of 2-chlorophenol and microbial contaminants in wastewater

In this work, a visible light active semiconductor photocatalyst ZnO-ZnS@polyaniline (ZnO-ZnS@Pani) nanocomposite was synthesized and its application was investigated for the photocatalytic degradation of organic and microbial contaminants in aqueous solution. The morphology and structural characteristics of the prepared materials were analysed using X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, Raman analysis and X-ray photoelectron spectroscopy. The photocatalytic activity of ZnO-ZnS@Pani was investigated for the degradation of 2-chlorophenol (2-CP) in synthetic wastewater under visible light irradiation as a function of contact time, pH and initial pollutant concentration. The highest 89% degradation of 2-CP was achieved at the pollutant concentration of 50 mg/L and 0.5 g/L catalyst dose. The efficient degradation was achieved due to the polyaniline in ZnO-ZnS@Pani nanocomposite which absorbs a wide range of visible light and inceases the eletron/hole separation. Moreover, the catalyst showed high stability and retained its photocatalytic activity up to the maximum level even after multiple reuses. Furthermore, ZnO-ZnS@Pani showed excellent antimicrobial action in sunlight against water born fecal E. coli, where 13.4% more effectiveness was observed as compared to ZnO-ZnS. These results revealed that ZnO-ZnS@Pani is an efficent visible light catalyst and can be used for the decontamination of wastewater.

Template-Free Synthesis of Monoclinic BiVO₄ with Porous Structure and Its High Photocatalytic Activity.

Monoclinic BiVO4 photocatalysts with porous structures were synthesized by a two-step approach without assistance of any templates. The as-prepared samples were characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS), photocurrent responses, and electrochemical impedance spectra (EIS). It is found that the as-prepared BiVO4 samples had a porous structure with aperture diameter of 50–300 nm. Moreover, the BET specific surface area of the porous BiVO4-200 °C sample reaches up to 5.69 m2/g, which is much higher than that of the sample of BiVO4 particles without porous structure. Furthermore, a possible formation mechanism of BiVO4 with porous structure was proposed. With methylene blue (MB) as a model compound, the photocatalytic oxidation of organic contaminants in aqueous solution was investigated under visible light irradiation. It is found that the porous BiVO4-200 °C sample exhibits the best photocatalytic activity, and the photocatalytic rate constant is about three times of that of the sample of BiVO4 particles without porous structure. In addition, the photocurrent responses and electrochemical impedance spectra strongly support this conclusion.

Cobalt-exchanged natural zeolite catalysts for catalytic oxidation of phenolic contaminants in aqueous solutions

Indonesia (IZ) and Australia (AZ) natural zeolites were employed to prepare cobalt exchanged catalysts. Characterization tests of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunaeuer-Emmet-Teller (BET) were used for performing sample analyses. The efficiencies of phenol removal on the catalysts were evaluated by the catalytic oxidation of phenol with sulfate radicals. Cobalt-exchanged catalysts showed higher phenol removal efficiencies than adsorption, Oxone self-oxidation and unmodified zeolites. The reactions were observed to be more efficiently described by the zero-order kinetics, while the respective Co/IZ and Co/AZ activation energies were 44.1 and 59.5. This study provides a novel application of low-cost natural zeolites for environmental remediation.

Facile fabrication of a direct Z-scheme Ag2CrO4/g-C3N4 photocatalyst with enhanced visible light photocatalytic activity

Graphite-like carbon nitride (g-C3N4) and silver-based compounds have attracted considerable attentions due to their excellent optical characteristic and photocatalytic performance. In this work, Z-scheme silver chromate-g-C3N4 nanosheets photocatalysts were prepared by binding growth of Ag2CrO4 nanoparticles on the surface of g-C3N4 nanosheets (g-C3N4-N) via a facile precipitation method. The morphologies, structure, specific surface area and optical property of the prepared photocatalysts were characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (UV-vis DRS) and photoluminescence (PL) spectra. The photocatalytic performances of the prepared Ag2CrO4/g-C3N4-N were evaluated by photodegradation of methyl orange (MO) and rhodamine B (RhB) under visible light irradiation (λ>400nm). The experiment results indicated that Ag2CrO4/g-C3N4-N composites presented enhanced photocatalytic activity and stability in the degradation of the dye contaminants in aqueous solution. The optimal composites with the mass ratio of Ag2CrO4 to g-C3N4-N as 50% (CNA-50) showed the highest photocatalytic activity for MO degradation, which is 5.9 and 10.8 times than those of pure Ag2CrO4 and pure g-C3N4-N, respectively. The formation of Ag2CrO4/g-C3N4-N Z-scheme heterojunction contributed to the improved photodegradation efficiency, which can not only promote the separation and transportation efficiencies of the photogenerated electron-hole pairs, but also present strong redox ability. And meanwhile the excellent transportation efficiency of the photogenerated electrons from Ag2CrO4 to g-C3N4-N greatly hindered the photocorrosion of Ag2CrO4 nanoparticles. This work provides a new understanding into the mechanism of the g-C3N4-N based composite and gives a new insight into the design and fabrication of Z-scheme photocatalysts.

Hierarchical carbon quantum dots/hydrogenated-γ-TaON heterojunctions for broad spectrum photocatalytic performance

There remains a pressing challenge in the efficient utilization of broad spectrum solar energy in the photocatalytic applications. Here we design and fabricate carbon quantum dots/hydrogenated-γ-TaON (CQDs/H-γ-TaON) hollow urchin heterojunctions that can enhance the UV–visible–NIR broad spectrum active photocatalytic property. Novel CQDs/H-γ-TaON photocatalysts have harnessed UV, visible, and near-infrared light to decompose organic contaminants in aqueous solution. Moreover, efficient photocatalytic hydrogen production as high as 496.5µmolh−1 with an apparent quantum efficiency of 12.2% under 420nm (about 61 times higher than that of conventional TaON) was achieved over CQDs/H-γ-TaON heterojunction, corresponding the order of hydrogen production rate: CQDs/H-γ-TaON>H-γ-TaON>γ-TaON. The improved UV and visible photocatalytic property can be attributed to high surface area from hollow nanostructures and efficient charge transfer based photoluminescence, electrochemical impedance and Mott–Schottky analysis. Especially, the NIR photocatalytic activity from the synergistic effects of the hydrogenation and the decoration of CQDs is ascribed to the efficient charge separation and transfer and up-converted photoluminescence property of CQDs that absorb NIR light and convert into visible light and transfer to visible-light photocatalytic H-γ-TaON. The CQDs/H-γ-TaON heterojunctions may open up more opportunities in the design of efficient broad spectrum active photocatalysts for environmental remediation and clean energy generation.

Chemical-activated carbons from peach stones for the adsorption of emerging contaminants in aqueous solutions

Activated carbons from peach stones by chemical activation with H3PO4(s) have been prepared, leading to high surface area and well-developed mesoporous materials. Further oxidation and gas phase treatments were applied in order to analyze the influence of the chemical surface groups on the adsorption behavior. The adsorption of three emerging compounds: a stimulant (caffeine), an anti-inflammatory drug (diclofenac) and a psychiatric drug (carbamazepine) from ultrapure water through batch and dynamic tests was investigated. The characterization of the adsorbents was conducted by N2 adsorption–desorption isotherms, scanning electron microscopy (SEM), infrared spectrometry (FTIR), thermal programmed decomposition (TPD), zero charge and isoelectric points (pHZPC, pHIEP) determination and the evaluation of the total acidity by potentiometric titration with n-butylamine. TPD profiles and FTIR spectra revealed the presence of carboxylic, phenolic, carbonyl and quinonic functionalities in the carbonaceous surfaces. S-type adsorption isotherms, as Giles classification, were obtained, indicating a competitive effect between aqueous solution and the target adsorbates. Carbamazepine adsorption capacity was higher than caffeine and diclofenac, reaching 335mg/g, attributed to its hydrophobic character and water solubility properties. The oxidation of the activated carbon greatly enhanced the hydrophilic character of the material, decreasing the adsorption capacity and highly affecting on the breakthrough times and adsorption capacity values in the fixed-bed adsorption process.

Carbon nanotubes and graphenes as adsorbents for adsorption of lead ions from water: a review

Nanomaterials have wide applications as sorbents for water purification as they have high selectivity as well as capacity for organic/inorganic pollutants and contaminants in aqueous solutions. Non-essential toxic heavy metals present in water have become a major cause of many diseases, ageing, and genetic problems. Carbon-based nanomaterials have generated great interest in their use as sorbent materials for removal of heavy metals from water/wastewater as they are stable, have limited reactivity, wide surface area, and are strong antioxidants. This study explored the possibility of ranking different carbon-based nanomaterials for efficient removal of lead ions from water which are routinely detected in water samples. Lead may be introduced in water because of its intensive use in many products. The adsorbents based on graphenes and carbon nanotubes have been analyzed on the basis of adsorption capacity, reusability, toxicity/biocompatibility, and cost. The effects of surface area of sorbent, pH of water, thermodynamics/kinetic studies have also been analyzed to evaluate the efficiency of sorbents. The information can be utilized to select the appropriate, most efficient and safe sorbents for removal of lead ions from water.