Laboratory Wastewater Research Articles

Pengaplikasian Kayu Apu (Pistia stratiotes L) Dalam Menurunkan Kadar BOD, COD dan TSS Pada Limbah Cair Laboratorium Di RSUD Besuki Kabupaten Situbondo

Hospital Laboratory wastewater contains organic compounds with a high enough concentration and possibly contain other chemical compounds and pathogenic microorganisms that can cause disease to the surrounding community. A way to overcome this problem is to do hospital laboratory liquid waste treatment. One alternative that can be used is the phytoremediation method using apu wood plants. Research on decreasing levels of BOD, COD and TSS in Besuki Public Hospital laboratory wastewater using Apu Wood (Pistia stratiotes L) was carried out in January - March 2019 with the aim to determine the decrease in laboratory wastewater BOD, COD and TSS after being given Apu (Pistia stratiotes L). The method used in treating liquid waste laboratory is phytoremediation. The results showed that after being treated as many as 10 treatments with the contact time of the apple plant for 1 day, 3 days and 6 days there was a significant decrease in BOD levels in the treatment with indigo P = 0,000 <0,05 for COD levels based on ANOVA output, known the value based on Anova sig table results is 0,000 <0,05 so it can be concluded that the average COD level after being treated is "DIFFERENT" significantly while the TSS parameter is ANOVA test with sig value 0,309> 0,05 which means "NO DIFFERENCE "Significantly on the treatment. It is recommended for further research, it should be endeavored to use plants that have resistance to waste, especially for contact time so that they can use higher waste concentrations with longer contact times. Keywords: BOD, COD, TSS, Apu Wood Plant (Pistia stratiotes L

The utility of cocoa pods husk M45 (Theobroma cocoa) as adsorbent of heavy metals, iron (Fe) and copper in the laboratory wastewater

Adsorption is one of the alternative media for processing wastewater. The study aims to use cocoa pods husk M45 (Theobroma Cacao) as a biosorbent in reducing Fe (III) and Cu (II) ions content in the laboratory liquid waste. This research was carried out through two systems, batch and continuous systems. The batch system was conducted to determine optimum contact time, optimum pH, and adsorption capacity, whereas the continuous system was intended to determine the adsorbent height and the maximum flow rate of laboratory liquid waste. The methods used in this study were adsorption and filtration. The adsorption results were analyzed by Atomic Absorption Spectrophotometer (AAS). The results found that the optimum contact time and the optimum pH for the adsorption of metal ions by cocoa pods husk M45 were 90 minutes and 6, respectively. The optimum flow rate of the wastewater in the continuous system was 6.166 mL/sec with an adsorbent height of 15 cm in the 2-inch adsorption column. The adsorption capacity of adsorbent based on the Langmuir isotherm was 11.074 mg/g for Fe (III) and 28.4091 mg/g for Cu (II).

Experimental and DFT studies on the selective adsorption of Pd(II) from wastewater by pyromellitic-functionalized poly(glycidyl methacrylate) microsphere

Palladium wastewater is produced from various industrial activities and seriously pollutes the environment. In here, a new adsorbent (PMDA-PGMA) was manufactured by functionalizing poly(glycidyl methacrylate) microspheres with pyromellitic acid and introduced to recover Pd(II) from wastewater. The main influencing factors including pH, palladium ionic content, reaction time and temperature were evaluated. The selectivity, reusability and sorption mechanism have been systematically examined. The pH 2 was optimal for Pd(II) adsorption and only 300 min was required to reach maximum adsorption capacity about 206.71 mg/g. The experimental data were is in tune with pseudo-secondary kinetics and Langmuir model well. So, the Pd(II) adsorption process was monolayer chemical adsorption. Thermodynamic parameters indicate that Pd(II) adsorption on PMDA-PGMA was an endothermic reaction. The main adsorption mechanism is ion exchange, electrostatic attraction and coordination between palladium ions and pyromellitic acid groups. Additionally, PMDA-PGMA can be easily regenerated by 10% thiourea and can be recycled at least five times. PMDA-PGMA exhibited good selective extraction ability for Pd(II) and effectively separated Pd(II) (≥95%) from laboratory wastewater in the presence divers metal ions. Density functional theory calculations show that PMDA-PGMA combines with Pd(II) through monodentate N atoms and bidentate O groups. The application prospect of PMDA-PGMA is encouraging in removing palladium from wastewater due to its high adsorption capacity and better reusability.

Selective recovery of gold ions in aqueous solutions by a novel trithiocyanuric-Zr based MOFs adsorbent

A trithiocyanuric-Zr based MOFs adsorbent (ZT-MOFs) was synthesized by using trithiocyanuric acid as a linker and zirconium chloride as a metal matrix and used to recover Au(III). ZT-MOFs was characterized by FT-IR, BET, Raman and FE-SEM. ZT-MOFs are porous material and have good stability in the range of pH 1–9. ZT-MOFs showed a higher adsorption capacity for Au(III) (333.34 mg/g) at 480 min and pH = 7. The experimental data fitted to Freundlich and pseudo second-order models, indicating a heterogeneous multi-layer chemadsorption is the dominated step. ZT-MOFs separated selectively Au(III) from laboratory wastewater containing various interfering ions. The removal rate of Au(III) decreased only from 94.5% to 87.5% after 4 adsorption and desorption cycles. This shows that ZT-MOFs have good repeatability. FT-IR, XPS and Zeta potential data shows that the adsorption mechanism of Au(III) on ZT-MOFs is coordination. Therefore, ZT-MOFs have great potential in extracting Au(III) from wastewater.

Using Bagasse and Aluminum Sulfate-Modified Bagasse as Adsorbents for Treatment of Industrial Cutting Fluid Wastewater in Laboratory and Pilot Scales

Industrial cutting fluid wastewater (CFW) is considered as hazardous substance due to its detrimental effects to the environment and workers welfare. Treatment of this type of wastewater was sometimes disregarded due to lack of knowledge and resources. However, adsorption, a straightforward approach, was used in this study to address this problem. The feasibility of the bagasse and modified bagasse in the adsorption of CFW was determined. Varying the adsorbent dosage resulted in an increase in the percent adsorption, whereas a decline for the adsorption capacity at equilibrium using a single-stage batch laboratory- and pilot-scale adsorption. The point of zero charge of the bagasse and the modified bagasse was measured to be at pH 5.5 and 2.4, respectively. The experiment also determined that, for a liter of CFW, 10.2 g and 59.2 g of the modified bagasse are required under laboratory- and pilot-scale systems, respectively. Isotherms of Langmuir, Freundlich, and Temkin were used in order to describe the adsorption process. It was determined that the surface heterogeneity and the pore size contributed to the adsorption of CFW; thus, Freundlich isotherm best fitted the data. Functional groups were verified using FTIR analysis and the heat of combustion, and their proximate analyses were determined. Based on the results under laboratory- and pilot-scale systems, modified bagasse is a viable material for the adsorption of CFW and solid fuel source.

REMOCIÓN DE MATERIA ORGÁNICA EN REACTOR ANAEROBIO DE MANTO DE LODOS DE FLUJO ASCENDENTE EN EL TRATAMIENTO DE AGUAS RESIDUALES DEL CAMAL DE HUANCAVELICA

En la presente investigación se evaluó un nuevo sistema de tratamiento primario para aguas residualesindustriales,se utiliza el “Reactor anaerobio de manto de lodos de flujo ascendente” (UASB), aplicado a la remoción de materia orgánica. El sistema a escala piloto fue diseñado para las aguas residuales del Camal Municipal de Huancavelica, el cual se bombeó después del pre tratamiento (cámara de reja gruesa y desarenador) al tanque de almacenamiento de 350 litros para realizar el tratamiento del agua residual en el reactor UASB a escala laboratorio. Se evaluó la eficiencia de remoción de materia orgánica en un reactor UASB, para un tiempo de retención hidráulico (TRH) de 14 horas con un caudal de circulación de 35mL/min se obtuvo una eficiencia mínima de remoción de Demanda Química de Oxígeno (DQO) de 33,66 % y una máxima eficiencia de 76,90 % todo ello en un rango de temperatura de agua residual de 10°C y 19°C. También para este TRH de 14 horas la cantidad de sólidos suspendidos totales disminuyó de 524,34mg/L a 365,04mg/L, obteniéndose una eficiencia de remoción de sólidos suspendidos totales de 30,28%. El tratamiento primario reactor UASB es una alternativa para remover la materia orgánica y sólidos suspendidos totales, aplicado para aguas residuales del Camal Municipal de Huancavelica y en localidades con condiciones de clima y altitud similares; el diseño se optimizó para un TRH de 14 horas para el reactor UASB el cual elevó la eficiencia de remoción de materia orgánica.

Efficient catalytic photodegradation of methylene blue from medical lab wastewater using MgO nanoparticles synthesized by direct precipitation method

Methylene blue is the main component of several stains such as Wright–Giemsa and Leishman stain that are used in histology and hematology laboratories. 97.8% of methylene blue from medical laboratory wastewater were photodegraded with the aid of MgO nanoparticles as photocatalysts and direct solar irradiation as a renewable source. The rate of photodegradation was 0.0184 min−1. The direct precipitation method was used as a simple and low cost method to synthesize MgO nanoparticles in the size range of 2.5–11.3 nm as estimated from X–ray diffraction peaks. The optical band gap energy was reduced to 4.25 eV. The photoluminescence spectra of MgO nanoparticles show four bands corresponding to F and F+ oxygen vacancy defects. The effects of the operational parameters (MgO dose, initial pH, irradiation source energy, initial concentration of the dye and temperature) were evaluated on the efficiency and rate of the photodegradation. The efficiency of the synthesized MgO nanoparticles was compared with TiO2 and ZnO nanoparticles as well.

Removal of Arsenic(III) from water using magnetite precipitated onto Douglas fir biochar

Magnetic Fe3O4/Douglas fir biochar composites (MBC) were prepared with a 29.2% wt. Fe3O4 loading and used to treat As(III)-contaminated water. Toxicity of As(III) (inorganic) is significantly greater than As(V) and more difficult to remove from water. Removal efficiency was optimized verses pH, contact time and initial concentration. Column sorption and regeneration were also studied. Adsorption kinetics data best fitted the pseudo second order model (R2 > 0.99). Adsorption was analyzed with three isotherm models at 20, 25 and 40 °C. The Sips isotherm showed the best fit at 25 °C with a 5.49 mg/g adsorption capacity, which is comparable with other adsorbents. MBC gave faster kinetics (~1–1.5 h) at pH 7 and ambient temperature than previous adsorbents. The Gibbs free energy (ΔG) of this spontaneous As(III) adsorption was −35 kJ/mol and ΔH = 70 kJ/mol was endothermic. Experiments were performed on industrial and laboratory wastewater samples in the presence of other co-existing contaminants (pharmaceutical residues, heavy metals ions and oxi-anions). The composite reduced the arsenic concentrations below the WHO's safe limit of 0.2 mg/L for waste water discharge. X-ray photoelectron spectroscopy (XPS) studies found As(III) and less toxic As(V) on Fe3O4 surfaces indicating adsorbed (or adsorbing) As(III) oxidation occurred upon contact with O2 and possibly dissolved Fe(III) or upon drying under oxic conditions. Under anoxic conditions magnetite to maghemite transformation drives the oxidation. A pH-dependent surface chemisorption mechanism was proposed governing adsorption aided by XPS studies vs pH.

Modified layered bimetallic compound used as a novel adsorbent for the solid-phase extraction of monoaromatic hydrocarbons from water samples prior to gas chromatography–mass spectrometry

This study reports a promising method of solid-phase extraction for determining the toluene, ethylbenzene, p-xylene, m-xylene, o-xylene, 1,3,5-trimethylbenzene, and 1,2,4-trimethylbenzene in water samples by gas chromatography–mass spectrometry (GC–MS). Prior to this procedure, the magnesium–aluminum bimetallic hydroxides modified with sodium dodecylbenzenesulfonate (Mg/Al-SDBS-LDH) were prepared and served as the novel solid-phase extractant. The Mg/Al-SDBS-LDH has advantage of good hydrophobicity and larger spacing which facilitates the monoaromatic hydrocarbons (MAHCs) into the interlayer for adsorption. As a result, the seven MAHCs in 500 mL water samples were enriched greatly, and the theoretical enrichment factor reached to 125 times. Under the optimized conditions of solid-phase extraction (SPE) and GC–MS, the mass concentration of each MAHC (0.005–10, 0.01–10, or 0.05–10 ng/mL) had a fine linear relationship with peak area. The correlation coefficients were more than 0.995. The detection limits were between 0.001 and 0.01 ng/mL, and the RSD were between 3.1% and 6.6%. The method had been applied to determine the seven MAHCs in the Dongfengqu river water and laboratory wastewater of Chengdu University of Technology successfully.

Selective recovery of Au(III) from wastewater by a recyclable magnetic Ni0.6Fe2.4O4 nanoparticels with mercaptothiadiazole: Interaction models and adsorption mechanisms

Abstract Gold is widely used in various industries. The recovery of Au(III) from wastewater has important economic and social benefits. In here, a new adsorbent (Ni0.6Fe2.4O4-MTD) was synthesized by functionalizing Ni0.6Fe2.4O4 with mercaptothiadiazole for selectively recovery of Au(III) from wastewater. The Ni0.6Fe2.4O4-MTD was characterized by FT-IR, TEM, ZETA, TGA and XPS. The optimum pH, kinetic, isotherm and thermodynamics were determined. The maximum adsorption capacity (283.9 mg/g) was obtained at pH 4 and 300 min. The mechanism was mainly ion exchange, complexation and reduction. The adsorption process submits to pseudo-secondary kinetics and Langmuir models because monolayer chemisorption is the rate-determining step. Adsorption and desorption experiments had shown that the adsorbent was reusable at least 4 cycles. In addition, Ni0.6Fe2.4O4-MTD can selectively separate Au(III) from laboratory wastewater containing various metal ions. The increase of temperature is favorable for Au(III) adsorption because adsorption processes were a spontaneous endothermic reaction. Since Ni0.6Fe2.4O4-MTD has high adsorption capacity and remarkable selectivity for Au(III), it becomes an ideal adsorbent for the recovery of Au(III) in wastewater.

Removal of triazines, triazoles and organophophates in biomixtures and application of a biopurification system for the treatment of laboratory wastewaters

Biopurification systems (BPS) have been barely explored for removing complex mixtures of pesticides. In this study, the potential of a biomixture to remove simultaneously a mixture of herbicides (triazines), fungicides (triazoles) and insecticides (organophosphates) is presented. Also, a BPS using the same biomixture was used for treating a pesticide testing laboratory wastewater containing a mixture of 38 compounds. Ecotoxicological assays were conducted on the BPS elutriates to investigate the mixture detoxification. A mixture (concentrations of 4–8 mg kg−1) run in small–scale biomixture systems (SSB) for 128 d showed 59.3% removal of triazines, 68.5% of organophosphates and no elimination of triazoles. The treatment of the laboratory wastewater (individual concentrations range: 0.0036–0.25 mg kg−1) in the pilot-scale BPS for 281 d resulted in the elimination pattern of organophosphates (90.0%) > triazoles (73.4%) > carbamates (71.3%) > triazines (54.3%). Complete detoxification towards Daphnia magna and partial detoxification in Lactuca sativa seeds germination occurred in the BPS. Although the pesticide mixture complexity is higher in the BPS, the lower concentrations found in this matrix, could explain removal differences between SSB and BPS and the apparent inhibition in the elimination of carbamates and some triazines observed in the latter. These findings suggest that disposal of pesticide–containing laboratory–wastewater should be done in separate containers, according to chemical groups before their treatment in separate BPS, in order to reduce treatment periods. Monitoring the treatment process in the BPS with a battery of ecotoxicological tests is strongly recommended.

The graphene oxide/magnesium–aluminium bimetallic hydroxides composite used as solid-phase extractant for determination of monoaromatic hydrocarbons in wastewater

ABSTRACT The graphene oxide (GO) and the magnesium–aluminium bimetallic hydroxides composite (GO/Mg-Al-LDH) was used as a solid-phase extractant for determination of toluene, ethylbenzene, p-xylene, m-xylene, o-xylene, 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene in wastewater by gas chromatography-mass spectrometry analytical method. When the amount of solid-phase extractant was 1.5 g, the extraction time was 6 min, and the elution with 2 mL of chloroform for 3 min, seven monoaromatic hydrocarbons (MAHCs) in 500 mL of water sample can be well extracted and separated. Under the optimised experimental conditions, the mass concentration of each component in the range of 0.01–5 ng/mL has a good linear relationship with the peak area, the coefficients of determination are all greater than 0.995. The relative standard deviation (n = 5) and the method detection limit range are 2.9–7.1% and 0.0005–0.005 ng/mL, respectively. The seven of MAHCs in Dongfengqu River and laboratory wastewater of Chengdu University of Technology can be effectively detected, the recovery rate and the relative standard deviation (n = 5) are 83.0–110.0% and 3.7–9.4%, respectively. For the first time, the GO/Mg-Al-LDH composite was used as a solid-phase extraction material, and seven MAHCs in water were successfully determined by GC-MS. The detection method is established with low detection limit and high reproducibility which can meet the measurement requirements of trace MAHCs in wastewater.

PG-PEI-Ag NPs-Decorated Membrane for Pretreatment of Laboratory Wastewater: Simultaneous Removal of Water-Insoluble Organic Solvents and Water-Soluble Anionic Organic Pollutants.

Generally, waste liquid in laboratory can be roughly classified into organic wastewater and inorganic wastewater. However, in some experiments, organic phase and water phase are inevitably mixed together, leaving the postclassification and disposal intractable. Traditionally, we used methods like distillation and extraction to separate these two phases, however, always consuming significant amounts of labor and time and meanwhile having an unsatisfactory separation efficiency. Here, we proposed an improved processing method with a propyl gallate (PG)-polyethyleneimine (PEI)-Ag nanoparticles (NPs)-decorated membrane, possessing the special wettability designed for organic and water phase separation. Accordingly, various kinds of organic solvents/water mixtures were tested, where the PG-PEI-Ag NPs-decorated membrane was used like a common filter paper, fixed onto the funnel of the waste liquid barrel. Afterward, the two phase mixtures were poured onto the membrane; as a result, the organic phase was blocked above while the water phase was left below. All kinds of organic solvents/water mixtures showed higher than 99.90% removal efficiency. Besides, the membrane can remove water-soluble anionic organic molecules through electrostatic interaction. Thus, along the phase separation, anionic organic molecules in water can be removed simultaneously. This pretreatment of lab wastewater with the PG-PEI-Ag NPs-decorated membrane is simple and efficient, relieving the pressure of postcollection and disposal to some extent.

High Adsorption Efficiency of Topkhana Natural Clay for Methylene Blue from Medical Laboratory Wastewater: a Linear and Nonlinear Regression

Local natural clay from Topkhana (Sulaimani district, Kurdistan region of Iraq) was characterized with XRD, XRF, FT-IR, and gas adsorption analyzer. The clay sample was dominated by saponite with minor amounts of chlorite. The clay was examined for its efficiency to adsorb and remove methylene blue (MB) from clinical laboratory wastewater by a batch method. The effects of pH, temperature, clay dosage, and initial MB concentration on the adsorption efficiency were investigated. The equilibrium experimental data were analyzed using Langmuir, Freundlich, Temkin, and Redlich-Peterson (R-P) isotherms. Most of the MB adsorption could be explained by cation exchange. The saponite, therefore, was the most important component in the clay. The rate of the adsorption process was found to follow pseudo-second-order kinetics. The conventional linear least squares method was compared with the more accurate method of non-linear curve fitting for the determination of isotherm and kinetic model parameters. Two error functions (the sum of the squared residuals and the correlation of determination) were used to evaluate the linear and non-linear regression analysis applied to the experimental data. Equilibrium thermodynamic parameters indicated a spontaneous and endothermic adsorption process.

Removal Methods of Heavy Metals from Laboratory Wastewater

The removal of heavy metals from the environment is the special concern due to their persistence without degradation. Methods for treating laboratory and industrial wastewater containing heavy metals often involve technologies for reduction of toxicity in order to meet technology-based treatment standards. Physico-chemical removal processes such as; adsorption on new adsorbents, ion exchange, membrane filtration, electrodialysis, reverse osmosis, and ultrafiltration were discussed. Their advantages and drawbacks in application were evaluated. In the processes of biological treatments microorganisms play a role of settling solids in the solution. Activated sludge, trickling filters, stabilization ponds are widely used for treating industrial wastewater. Bioadsorption is a new biological method and various low cost bioadsorbents (agricultural waste, forest waste, industrial waste, algae etc.) are used for maximum removal of heavy metals from wastewater. Bioadsorption techniques are eco friendly best solutions for removing heavy metals from wastewater rather than physic-chemical methods. But chemical methods are most suitable treatments for toxic inorganic compounds produced from various industries which cannot removed from any biological and physical techniques. Keywords: Heavy metals; removal techniques; Bioadsorption; physico-chemical treatments DOI : 10.7176/JNSR/9-2-04

Pengelolaan Kandungan Bahan Organik pada Limbah Cair Laboratorium ProlingMSP-IPB dengan Berbagai Kombinasi Agen Bioremediasi

ABSTRACT Wastewater from laboratory glassware washing activities contains organic materials. Decomposing bacteria could increase the biomass by utilizing organic matter as a source of carbon. This research was aimed to describe the influence of commercial probiotic application in reducing organic matter content of Proling laboratory wastewater. The research was conducted from February to July 2016 in Aquatic Microbiology Laboratory. The experiment consists of several treatments, those were wastewater (L), wastewater+molase (LM), and wastewater+molase+bacteria from commercial probiotic (LMB). Major parameters observed were COD and bacteria abundance. The results showed that there was significant response difference between molasses and without molasses treatment. Based on COD, the most influenced treatment in decreasing organic matter were LM and LMB. These treatments could decrease COD up to 97% and 91%. Furthermore, the abundance of bacteria in molasses treatment was higher than without molasses. Based on this study, the most effective treatment in reducing organic matter was LMB. Keywords: bacteria, laboratory wastewater, molasses, organic matter

Adsorption of Common Laboratory Dyes Using Natural Fibers from Luffa cylindrica

Adsorption of methylene blue and malachite green was carried out using Luffa cylindrica sponges as adsorbing material. We provide a very illustrative exercise about the use of common natural materials requiring little preparation to solve environmental tasks in a routine laboratory situation such as using dyes. In addition, the experiment can be used in different study levels. We illustrate the use of spectrophotometric techniques, calibrations, or (in a more advanced level) calculations of adsorption kinetics and the use of statistical tools in data treatment. The use of natural fibers to remove dyes from laboratory wastewater highlights the environmental responsibility of undergraduate students by training them to treat common laboratory pollutants, and on the other hand, it offers an efficient tool to illustrate water remediation procedures.

Integration of treatment technologies with Fenton reagent for laboratory effluent remediation

This study investigated of the potential value of the integration of the coagulation/flocculation, Advanced Oxidation Processes (AOP) (Fenton reagent) and slow sand filtration technologies, with the aim of treating laboratory wastewater. The treatment system was designed in laboratory scale through coagulation/flocculation. It involved the use of Jar Test equipment with a sequence of two rotational phases: fast mixes to 300 rpm for 20 seconds and slow mixes to 30 rpm for 6 minutes and 10 seconds, with the addition of anionic polymer and sedimentation for 60 minutes at ambient temperature. In the treatment via Fenton reagent, two rotational phases were used: rapid mixing at 300 rpm for 20 seconds with the addition of iron (Fe2+) and slow mixing at 30 rpm for 6 minutes and 10 seconds with the addition of hydrogen peroxide, followed by 60 minutes of sedimentation at ambient temperature. A cylindrical tank of polyvinyl chloride, sands and non-woven synthetic fabrics were used in the slow filtration. The filtration rate adopted was 3 m3 m-2 d-1 with a hydraulic retention time of 264 minutes. The best concentrations of chemical reagents used in the treatments were: 0.80 mg L-1 of polymeric anionic, 200.00 mg L-1 of H2O2 and 13.00 mg L-1 of total soluble iron. The integration of the treatment technologies made it possible to achieve a removal rate of 75.27% of COD and 94.12% of total phenols. Furthermore, the conjugation of the processes allowed the removal of 87.58% of TOC.

Selective recovery mechanism of Au(III) from an aqueous solution by trimethyl phosphate modified poly(glycidyl methacrylate)

Abstract A new adsorbing material (PE-PGMA) was prepared by grafting trimethyl phosphate onto poly(glycidyl methacrylate), and it was applied to selectively adsorb gold ions from an aqueous solution. FT-IR (Fourier transform infrared spectroscopy), SEM (scanning electron microscopy), XPS (X-ray photoelectron spectroscopy) and zeta potential analysis were employed to characterize the prepared adsorbent. Three kinetic and isothermic equations were employed to investigate the selective adsorbing mechanism of Au(III) from an aqueous solution. The adsorbent had the highest adsorption rate in the pH range from 2 to 9, thus suggesting that PE-PGMA had a wide acid-base tolerance. The adsorbing equilibrium is attained in 10 min and the maximum adsorption capacity is 601.34 mg/g. The pseudo-second-order and Langmuir models well described the kinetics and isotherms of the adsorption process, respectively. The results certified that the adsorbing process was monolayer sorption and the rate-limiting step was chemical adsorption. After seven cycles of reusability experiments, the adsorbing rate of gold ions decreased from 99.06% to 96.72%, thus proving that the adsorbent has good reusability. Moreover, the adsorbent presented good selectivity for gold ions from the coexisting ions (Cu2+, Ni2+, Co2+, Ge4+ and Pb2+). The chelation interaction between phosphate groups and Au(III) played a significant role in the selective adsorption and higher uptake capacity. Furthermore, the column adsorption and the recovery experiment of gold from laboratory wastewater demonstrated that the PE-PGMA has good potential to recover gold.

Facial fabrication of carbon quantum dots (CDs)-modified N-TiO2-x nanocomposite for the efficient photoreduction of Cr(VI) under visible light

In this study, for the first time, a novel CDs-N-TiO2-x nanocomposite was successfully fabricated by decorating the carbon quantum dots (CDs) on the nitrogen (N) and Ti3+ codoped TiO2 nanoparticles using a facile hydrothermal-calcination method. X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS), electron paramagnetic resonance (EPR) spectra, and X-ray photoelectron spectroscopy (XPS), etc., were utilized to investigate the physicochemical properties of the catalyst and to confirm the successful introduction of CDs and the formation of N/Ti3+ codoping levels in the nanocomposite. Owing to the synergy between the modification of CDs and codoping of N and Ti3+, the as-prepared CDs-N-TiO2-x nanocomposite exhibited enhanced visible light absorption and more efficient charge separation compared with its counterparts, such as the pristine TiO2, N-doped TiO2 (N-TiO2), N and Ti3+ codoped TiO2 (N-TiO2-x), and carbon quantum dots-TiO2 (CDs-TiO2), etc. As a result, the CDs-N-TiO2-x nanocomposite displayed a remarkable performance for Cr(VI) reduction under visible light irradiation. Moreover, adding the appropriate amount of citric acid as the hole scavenger significantly increased the reduction rate of Cr(VI). In addition, the reduction efficiency was better under acidic conditions and considerably affected by the initial Cr(VI) concentration and catalyst dosage. Thermogravimetric analysis and cyclic runs demonstrated a unique thermal and chemical stability of the CDs-N-TiO2-x nanocomposite. The mechanism of the enhanced photoreduction of Cr(VI) by the CDs-N-TiO2-x nanocomposite was discussed based on all the characterization and experimental results. Moreover, the developed CDs-N-TiO2-x nanocomposite also exhibited efficient photocatalytic performance to reduce the Cr(VI) contained in real laboratory wastewater.