FROM SAMPLING TO PURIFICATION: METHODOLOGIES AND TECHNIQUES FOR EVALUATION OF SILOXANES IN BIOGAS. Biogas has emerged as an important source of clean and renewable energy, with its energy viability dependent on purity grade. Primarily composed by methane and carbon dioxide, biogas can also contain nitrogen, water vapor, oxygen, hydrogen sulfide, ammonia, hydrocarbons and siloxanes. Regarding methane, all other components are considered contaminants, with volatile methylsiloxanes (VMSs) being the major challenge in terms of control and removal. VMSs are commonly found in personal care products and industrial applications, and their presence is highly detrimental to biogas energy generation equipment by forming silica deposits that cause fouling and damage, reducing operational efficiency and system longevity. In this context, three topics are crucial: (i) sampling techniques (bags, gas cylinders, canisters, adsorbent tubes, and impingers); (ii) detection and quantification methods for VMSs, highlighting gas chromatography coupled with mass spectrometry; and (iii) biogas purification/removal strategies (adsorption, absorption, refrigeration/condensation, biological degradation, and membrane separation). This review explores the methodologies involved in these topics, presenting literature research approaches and their effectiveness regarding siloxanes, contributing to biogas applications.

Novel nanocomposites synthesized with pollen grain, as a precursor, were tested for CO2 adsorption performance. The pollen-derived carbons were obtained by direct calcination (PC), calcination followed by KOH-chemical activation (PCKOH), and MgO incorporation using high-energy ball-milling (PC-MgO and PCKOH-MgO). All the as-prepared materials were texturally, morphologically and structurally characterized by N2 physisorption, scanning electron microscopy (SEM-EDS) and X-ray diffraction (XRD); CO2 adsorption/desorption was measured by thermogravimetry. The four materials were able to adsorb CO2 at 30 ºC and 1 bar, but PCKOH-MgO, with the high surface area (12.4 m2 g-1), total pore volume of (0.13 cm3 g-1) and microporosity, was the best (2.06 mmol g-1 and percentage of adsorption (Qad) = 9.06%, at 1 bar). This result is due to the synergic effect of both synthesis methods. Neither temperature (from 30 to 100 ºC), nor pressure (from 1 to 15 bar), improved the adsorption process of PCKOH-MgO. CO2 desorption times at 300 ºC were 47 min for PCKOH-MgO and 30 min for the other adsorbents, showing the possibility of cycling. Based on the obtained results, the PCKOH-MgO activated carbon nanocomposite stands as a promising adsorbent to be potentially used for industrial CO2 capture applications and to contribute to long-term solutions to avoid dangerous climate-change and reduce CO2 emissions. grain precursor CO performance pollenderived derived PC, PC , (PC) KOHchemical KOH chemical PCKOH, PCKOH (PCKOH) highenergy energy ballmilling ball milling PCMgO PCKOHMgO. PCKOHMgO . PCKOH-MgO) asprepared prepared texturally N physisorption SEMEDS SEM EDS (SEM-EDS Xray X ray XRD (XRD) adsorptiondesorption thermogravimetry 3 bar PCKOHMgO, MgO, 12.4 124 12 4 (12. m g1, g1 g 0.13 013 0 13 (0.1 cm microporosity 2.06 206 2 06 (2.0 g- Qad (Qad 906 9 9.06% bar. bar) methods from 10 ºC, ºC) MgO. adsorbents cycling results longterm long term climatechange climate change emissions (PC (PCKOH (XRD 12. (12 0.1 01 (0. 2.0 20 (2. 90 9.06 (1 0. (0 2. (2 9.0 ( 9.

Palygoskite pellets were synthesized with lignin and WAX® and subjected to technological characterization for application in the remediation of Pb ions contained in aqueous effluents. X-ray diffraction (XRD) characterization of the palygorskite:lignin:WAX® material in a proportion of 70:15:15 revealed that the heat treatment of the pellets did not compromise the crystalline structure of the palygoskite. Texture analyses demonstrated that the surface area increased after synthesis and heat treatment, thus increasing the adsorption capacity. Regarding porosity, X-ray microtomography revealed that the pellets exhibit an irregular and porous spherical morphology with interconnected pores. Adsorption tests showed a removal of 73% of PbII contained in aqueous effluents after 15 min, with equilibrium reached in 60 min (88.36%). After the adsorption process, the presence of lead in the material was qualitatively confirmed through scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) images. The produced pellets exhibit promising adsorbent qualities, such as strength and effective PbII ion adsorption. WAX Xray X ray XRD (XRD palygorskiteligninWAX® palygorskiteligninWAX palygorskite palygorskite:lignin:WAX 701515 70 70:15:1 palygoskite capacity porosity pores 73 1 6 88.36%. 8836 88.36% . 88 36 (88.36%) process energydispersive energy dispersive SEMEDS SEM EDS (SEM-EDS images qualities 70151 7 70:15: 883 88.36 8 3 (88.36% 7015 70:15 88.3 (88.36 701 70:1 88. (88.3 70: (88. (88 (8 (

In this work, using the PM3 semi-empirical method, the oxidation of the single-walled carbon nanotube (SWCNT) was studied by sulfuric and nitric acid for the incorporation of carbonyl (C=O), phenol (OH) and carboxylic (COOH) groups in the C=C bonds present on the surface of the nanotube. Subsequently, the crosslinking of the oxidized SWCNT (SWCNTox) and chitosan (Q) was observed through hydrogen bonds of the C=O and OH bonds with 2.34 Å, the process was endothermic and soluble in polar solvents due to the presence of OH and NH groups in the structure of SWCNTox/Q. The Monte Carlo modeling allowed to study the adsorption of pesticides in the SWCNTox/Q at different temperatures, where the QSAR (quantitative structure activity relationship) properties allowed predicting the behavior of the pesticides, that is, the degree of hydrophobicity (log P) and accessible surface area (ASA) were important parameters in the evaluation of SWCNTox/Q as an adsorbent and surface interacting with pesticides respectively. Finally, the adsorption was a physisorption process due to the electronegativity of the CO, OH, NH2, NH and C=O bonds. work PM semiempirical semi empirical method singlewalled single walled (SWCNT C=O, CO , C O (C=O) (OH COOH (COOH CC Subsequently SWCNTox (SWCNTox Q (Q 234 2 34 2.3 Å SWCNToxQ temperatures quantitative relationship is log P ASA (ASA respectively Finally NH2 (C=O 23 3 2.

This research aims to develop a precise and efficient dispersive solid-phase microextraction (DSPE) technique using third-generation polyamidoamine (PAMAM) dendrimer-grafted nanoparticles to quantify benzoylurea pesticides in green tea, black tea, and oolong tea infusions. The extraction efficiency is optimized through single-factor adjustments of key parameters, including adsorbent quantity (5-20 mg), adsorption duration (5-20 min), desorbent identity (methanol, acetonitrile), volume (100-600 μL), sodium chloride concentration (0-10%, m/v), and sample solution pH (3-8). The optimized method demonstrates linearity in the range of 2-500 μg L-1, with limits of detection (LODs) ranging from 0.6-1.5 μg L-1 and limits of quantification (LOQs) from 2.0 5.0 μg L-1. Recovery rates of 81.2-96.0% are achieved, with intra-day relative standard deviations (RSDs) of 1.4-2.8% and inter-day relative standard deviations of 2.0-3.9%, indicating high accuracy and repeatability. The successful application of detecting residues in commercial tea samples underscores the strong potential of the technique to determine benzoylurea analyte levels. solidphase solid phase DSPE (DSPE thirdgeneration third generation PAMAM (PAMAM dendrimergrafted dendrimer grafted infusions singlefactor single factor parameters 520 5 20 (5-2 mg, mg , mg) min, min min) methanol, methanol (methanol acetonitrile, acetonitrile acetonitrile) 100600 100 600 (100-60 μL, μL μL) 010%, 010 0 10%, 10 (0-10% m/v, mv m/v m v m/v) 38. 38 3 8 . (3-8) 2500 2 500 2-50 L1, L1 L 1, 1 LODs (LODs 0.61.5 0615 0.6 1.5 6 0.6-1. L- LOQs (LOQs 2. 50 5. L1. 1. 81.296.0% 812960 81.2 96.0% 81 96 81.2-96.0 achieved intraday intra day RSDs (RSDs 1.42.8% 1428 1.4 2.8% 4 1.4-2.8 interday inter 2.03.9%, 2039 3.9%, 9 2.0-3.9% repeatability levels 52 (5- 10060 60 (100-6 010% 01 10% (0-10 (3-8 250 2-5 61 0.61. 061 06 0. 15 0.6-1 296 81.296.0 81296 812 81. 960 96.0 81.2-96. 42 1.42.8 142 14 28 2.8 1.4-2. 03 2.03.9% 203 39 3.9% 2.0-3.9 (5 1006 (100- (0-1 (3- 25 2- 0.61 0.6- 29 81.296. 8129 96. 81.2-96 1.42. 1.4-2 2.03.9 3.9 2.0-3. ( (100 (0- (3 81.296 81.2-9 1.42 1.4- 2.03. 3. 2.0-3 (10 (0 81.29 81.2- 2.03 2.0- (1

Nanocomposites of GO/γ-Fe2O3 were used for magnetic dispersive solid-phase microextraction (m-d-μ-SPE) of six pesticides from river water samples, followed by the determination using high performance liquid chromatography-diode array detection. The synthesis of the nanocomposites is described and characterized using Fourier transform-infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. A central composite design was used to optimize the extraction time, sample solution pH, and adsorbent amount. The solvent type and volume for desorption and the effect of the ionic strength for adsorption were also investigated. The optimum adsorption conditions were achieved at 84 min of extraction time, pH 5.4, 115 mg of absorbent, and 1% (m/v) of NaCl, while the desorption solvent selected was 1.0 mL of methanol-acetic acid (9:1, v/v). The limits of detection ranged from 0.1 to 0.9 μg L-1, and a good precision was achieved with relative standard deviation (RSD) lower than 7.6% (n = 10). The accuracy of the method was accessed by recovery tests ranging from 82 to 117% (n = 3, RSD < 8%). GO/γFe2O3 GOγFe2O3 GOγFeO GO/γ Fe2O3 GO γ Fe O GO/γ-Fe2O solidphase solid phase mdμSPE m d μ SPE (m-d-μ-SPE samples chromatographydiode chromatography diode transforminfrared transform infrared spectroscopy Xray X ray diffraction microscopy time amount investigated 8 54 5 4 5.4 11 absorbent 1 m/v mv v (m/v NaCl 10 0 1. methanolacetic methanol acetic 91, 91 9 1, (9:1 v/v. vv v/v . v/v) 01 0. 09 L1, L1 L L-1 (RSD 76 7 6 7.6 n 10. 10) 117 3 8%. 8% 8%) γFe2O3 γFe GO/γFe2O GOγFe GOγFe2O GOγ FeO Fe2O 5. (9: L- 7. γFeO γFe2O (9 (

Jaboticaba peel powder (JPP) is a residue that contains phenolic compounds, such as anthocyanins and gallic acid. An adsorbent-bioactive complex (ABC) was synthesized using an extract rich in compounds with antioxidant properties obtained from JPP immobilized on microcrystalline cellulose from sweet sorghum bagasse. In this work, the result of thermal degradation of anthocyanins from JPP and ABC, activation energy (Ea), half-life time (t1/2), decimal reduction time (D), temperature variation (Z), thermodynamic parameters (enthalpy (ΔH), Gibbs free energy (ΔG) and entropy (ΔS)) and degradation of antioxidant activities were investigated. Anthocyanin degradation of 35, 60 and 85% was observed for JPP and 10, 30 and 65% for ABC at temperatures of 90-130 °C. Ea of JPP and ABC were 110 and 91 kJ mol-1, respectively. ABC was able to increase from 143-690% the half-life time when compared to JPP. The Z parameter indicated that a greater temperature variation is necessary to degrade ABC anthocyanins (31 °C) when compared to JPP (25 °C). The thermodynamic parameters showed that the energy needed to be broken down to reach the transition state is higher for JPP than ABC, in addition ABC is closer to its thermodynamic equilibrium state. Thus, ABC can be used as an additive in pharmaceutical, cosmetics and food industries, maintaining bioactive and antioxidant properties. (JPP acid adsorbentbioactive adsorbent (ABC bagasse work Ea, , (Ea) halflife half life t1/2, t12 t t1/2 t1 2 (t1/2) D, D (D) Z, (Z) enthalpy ΔH, ΔH (ΔH) ΔG (ΔG ΔS (ΔS) investigated 35 6 85 10 3 65 90130 90 130 90-13 C °C 11 9 mol1, mol1 mol 1, 1 mol-1 respectively 143690% 143690 143 690% 690 143-690 31 (3 25 (2 . Thus pharmaceutical industries (Ea t1/ (t1/2 (D (Z (ΔH (ΔS 8 9013 13 90-1 mol- 14369 14 69 143-69 ( (t1/ 901 90- 1436 143-6 (t1 143- (t

This study investigated the removal of contaminants in water by adsorption on thermoplastic starch (TPS) and kraft lignin (KL) composites. A study on the desorption of methylene blue (MB) and methyl orange (MO) dyes in water was also carried out, followed by the photodegradation of solutions containing dissolved dyes. Initially, the surface morphology of the TPS and TPS-KL films was analyzed by scanning electron microscopy, revealing advantageous characteristics for efficient adsorption of contaminants. Fourier transform infrared spectroscopy (FTIR) analysis made it possible to characterize the TPS and TPS-KL composites. The results demonstrate the reversibility of the process and confirm the lack of permanent chemical modification in the polymer matrix, indicating that the adsorption/desorption process is physical rather than chemical. This suggests that the adsorbent material can be reused without losing its fundamental structural properties. Furthermore, the study allows for verification of the chemical changes on the surfaces of the materials involved. Ultraviolet-visible spectroscopy (UV-Vis) results show that for MO, both substrates exhibited low adsorption capacity, with efficiency values close to 20%. In contrast, for MB, both composite materials displayed excellent dye adsorption rates, achieving efficiencies of 78% or higher. The photodegradation of adsorbed dyes revealed promising results. (TPS KL (KL composites MB (MB MO (MO out Initially TPSKL microscopy FTIR (FTIR matrix adsorptiondesorption properties Furthermore involved Ultravioletvisible Ultraviolet visible UVVis UV Vis (UV-Vis capacity 20 20% contrast rates 78 higher 2 7

The use of materials such as organofunctionalized silica for application in solid phase extraction (SPE) allows the preconcentration of several ions, including Pt, and subsequent detection. This work aims to synthesize and characterize an organofunctionalized silica (Sil-TMSDT) with the silylant N’(trimethoxysilyl)propylethylenetriamine and its application as a solid phase in the preconcentration Pt4+ ions in aqueous media, using detection by flame atomization atomic absorption spectroscopy (FAAS). The Fourier-transform infrared spectroscopy (FTIR) spectra and scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS) confirmed the aminofunctionalization of the silica. For the adsorption process, a preconcentration mini-column with 200 mg of Sil-TMSDT, a solution of 0.485 mg L−1 of K2[PtCl6] at pH 10 and HNO3 0.5 mol L−1 as eluent were used, obtaining an enrichment factor of 15-fold with retention efficiency higher than 99%. The Pt4+ ion determined by FAAS showed a linear response between 0.02 and 0.40 mg L−1; a linear coefficient where R = 0.9981; a 16-fold preconcentration factor; a limit of quantification (LOQ) and limit of detection (LOD) of 0.045 and 0.014 mg L−1, respectively. The proposal system showed analytical applicability to determining Pt4+ ion in an aqueous medium and could be used to detect traces of this potentially toxic metal in biological fluids such as urine and blood. SPE (SPE Pt SilTMSDT Sil TMSDT (Sil-TMSDT Ntrimethoxysilylpropylethylenetriamine N trimethoxysilyl propylethylenetriamine Pt4 media FAAS. . (FAAS) Fouriertransform Fourier transform FTIR (FTIR SEM (SEM energydispersive energy dispersive EDS (EDS process minicolumn mini column 20 SilTMSDT, TMSDT, Sil-TMSDT 0485 0 485 0.48 L1 L 1 L− K2PtCl6 KPtCl K2 PtCl6 K PtCl K2[PtCl6 HNO 05 5 0. 15fold fold 15 99 99% 002 02 0.0 040 40 0.4 0.9981 09981 9981 16fold 16 LOQ (LOQ LOD (LOD 0045 045 0.04 0014 014 0.01 respectively blood (FAAS 2 048 48 K2PtCl K2[PtCl 9 00 04 4 0.998 0998 998 004 001 01 0.99 099 0.9 09

Abstract:The growing demand of the housing sector in the city of Machala-Ecuador turned invasions into the common model of disorganized growth of this city, where they use the “El Macho” estuary for the disposal of waste and sewage. Preliminary studies regarding the content of heavy metals in this estuary conclude that the concentrations of metals such as cadmium are higher than the limits established in the regulations of the Unified Text of Secondary Legislation of the Ministry of the Environment. In the present investigation, the removal of cadmium from water samples of the “El Macho” estuary was evaluated using polyurethane foam activated with silver nanoparticles as an adsorbent. To collect adsorption data, a vertical tubular reactor was designed, using 1,560 g of polyurethane adsorbent modified with silver nanoparticles, pH 8 and cubic-shaped polyurethane foam size of 0.5 cm of side. Cadmium concentrations were quantified by atomic absorption spectroscopy in samples of Estero water before and after passing through the reactor. It is concluded that the polyurethane foam activated with silver nanoparticles, as an adsorbent, reached a removal percentage of 48.75% and therefore, it is effective for the treatment of water contaminated with cadmium.

Resumen:La demanda creciente del sector vivienda en la ciudad de Machala-Ecuador convirtió a las invasiones en el modelo común de crecimiento desorganizado de esta ciudad, donde utilizan el estero “El Macho” para la eliminación de desechos y aguas negras. Estudios preliminares respecto al contenido de metales pesados en este estero concluyen que las concentraciones de metales como el cadmio son superiores a los límites establecidos en la normativa del Texto Unificado de Legislación Secundaria del Ministerio del Ambiente. En la presente investigación se evaluó la remoción de cadmio de muestras de aguas del estero “El Macho” utilizando espuma de poliuretano activada con nanopartículas de plata como adsorbente. Para la recolección de los datos de adsorción se diseñó de un reactor tubular vertical, utilizando 1,560 g de adsorbente de poliuretano modificado con nanopartículas de plata, pH 8 y tamaño de la espuma de poliuretano de forma cubica de 0,5 cm de lado. Se cuantificó las concentraciones de cadmio mediante espectroscopia de absorción atómica, en muestras de aguas del Estero antes y después de su paso por el reactor. Se concluye que la espuma de poliuretano activada con nanopartículas de plata, como adsorbente, alcanzó un porcentaje de remoción de 48,75% y, por lo tanto, es efectivo para el tratamiento de aguas contaminadas con cadmio.

RESUMEN: El río Tumbes es la principal fuente de agua de la ciudad del mismo nombre en el noroeste del Perú. Sin embargo, en las condiciones actuales recibe la influencia de actividades como la minera artesanal en la parte alta de la cuenca, contaminándolo con metales pesados como el plomo, el cual es potencialmente causante de enfermedades. Por otro lado, el sillar (ignimbrita) es un material de construcción extraído en la ciudad de Arequipa que en el momento de ser cortado en bloques causa un material residual que normalmente es desechado. El objetivo de esta investigación es producir y caracterizar materiales adsorbentes basados en sillar para remover directamente Pb del agua del río Tumbes. El sillar se llevó a tamaños de partícula de 150 µm y 250 µm, y fueron activados por pirolisis lenta con y sin presencia de ZnCl2, para luego ser impregnadas con nanopartículas (NPs) de ZnO utilizando la técnica de impregnación in situ. El tratamiento térmico logro modificar la estructura de los materiales, aumentando la fase cristalina de los mismos, sin embargo, aparentemente la concentración de NPs de ZnO impregnada sobre las muestras de sillar pirolizado fue muy reducida para ser detectada por difracción de rayos X. En las pruebas de cinética de adsorción de Pb utilizando directamente de muestras de agua del rio Tumbes, se demostró que los adsorbentes basados en sillar presentaron limitada capacidad de adsorción comparada con otros adsorbentes derivados de rocas, obteniendo valores de adsorción de entre 0,009 - 0,017 mg de Pb/g del adsorbente. Sin embargo, las concentraciones finales luego de los experimentos de adsorción se encentraron por debajo del límite de 0,05 mg/l establecido por la OMS para el caso de agua potable. A pesar de ello es importante el estudio a mayor profundidad con diversos tipos de sillar y otros tipos de modificaciones para corroborar el potencial uso del sillar como adsorbente.

ABSTRACT: Tumbes River is the main source of water for the city of the same name in northwest Peru. However, under current conditions it is negatively affected by activities such as artisanal mining in the upper part of the basin. It causes water pollution with heavy metals such as lead, which is potentially a cause of chronic diseases. On the other hand, ignimbrite is a volcanic rock extracted in the city of Arequipa. It is used as construction material and when it is cut into blocks, produces residual material that is normally discarded. This research aimed to produce and characterize adsorbent materials based on ignimbrite to directly remove Pb from the water of the Tumbes River. The ignimbrite was used in particle sizes of 150 µm and 250 µm, and the materials were activated by slow pyrolysis with and without the presence of ZnCl2. Then thermal treatment, the materials were impregnated with ZnO nanoparticles (NPs) using the in-situ impregnation technique. The thermal treatment manages to modify the structure of the materials, increasing their crystalline phase; however, apparently the concentration of ZnO NPs impregnated on the pyrolyzed ignimbrite samples was too low to be detected by X-ray diffraction. In the Pb adsorption kinetic tests using water samples directly from the Tumbes River, it is shown that adsorbents based on ignimbrite showed limited adsorption capacity compared to other adsorbents derived from rocks, obtaining adsorption values between 0.009 - 0.017 mg of Pb/g of the adsorbent. However, the final concentrations after the adsorption experiments were below the limit of 0.05 mg/l established by the WHO for drinking water. Despite this, it is important to conducted experiments using other types of ignimbrite and other types of modifications to corroborate the potential use of ignimbrite as an adsorbent.

RESUMEN El Camalote es un pasto perenne que se reproduce rápido y espontáneamente en regiones tropicales. Este pasto no tiene ningún aprovechamiento económico; por el contrario, se le considera una maleza. Sin embargo, es una buena fuente de celulosa y se da en abundancia. En este sentido, el propósito de este trabajo es aprovechar al pasto Camalote como adsorbente del azul de metileno (AM). Las pruebas de adsorción se realizaron en sistema de proceso por lotes, utilizando concentraciones de AM en un rango de 20 a 100 mg/L. La más alta capacidad de adsorción (qe) fue de 43 mg/g para la concentración de 100 mg/L de AM a un pH de 8. Para todas las concentraciones estudiadas se obtuvieron valores de porcentaje de remoción mayor a 80 % en un tiempo de contacto de 30 minutos. Los datos de equilibrio se correlacionaron con los modelos de Langmuir y Freundlich. Los valores de qmax para la isoterma de Langmuir se encuentran en el rango de 19,79 a 94,51 mg g-1 y b entre 0,10 a 0,05 L mg-1. Mientras que para la isoterma de Freundlich se obtienen valores de K que van de 3,79 a 5,13 (mgg-1(L mg-1)-1/n y n entre 2,6 y 1,27, lo que indica que en los sitios activos el AM se retiene por quimisorción, a través de puentes de hidrógeno. Los resultados demostraron que el pasto Camalote en un material eficiente y económicamente viable para remover colorantes de medios acuosos.

ABSTRACT Camalote is a perennial grass that reproduces quickly and spontaneously in tropical regions. This grass has no economic use; on the contrary, it is considered a weed. However, it is a good source of cellulose and occurs in abundance. In this regard, the purpose of this work is to take advantage of the Camalote grass as an adsorbent of methylene blue (MB). The adsorption tests were carried out in a batch system, using MB concentrations within the range of 20-100 mg/L. The highest adsorption capacity (qe) was 43 mg/g for the concentration of 100 mg/L of MB at pH 8. For all the concentrations studied, percentage removal values greater than 80% were obtained in a contact time of 30 min. The equilibrium data were correlated with the Langmuir and Freundlich models. The qmax values for the Langmuir isotherm are within the range of 19.79 to 94.51 mg g-1 and b from 0.10 to 0.05 L mg-1. While for the Freundlich isotherm, K values ranging from 3.79 to 5.13 (mgg-1(L mg-1)-1/n and n from 2.6 to 1.27 are obtained, suggesting that in the active sites MB is retained by chemisorption through hydrogen bonds. The results showed that Camalote grass is an efficient and economically viable material for removing dyes from aqueous media.

Flouride contamination of water is recognised as a serious challenge facing humanity. Consumption of water that contains excessive amounts of fluoride can result in fluorosis. Consequently, concerted efforts have been made to develop cheap, effective and green techniques/materials to remove fluoride from water, particularly potable water. Bone char prepared from bovine, swine, and equine bones has been used extensively in this regard, and is the most promising, cheap and green material for treating drinking water with high fluoride concentration, particularly in developing countries. However, research on bone char prepared from bones of animals in the wild, as well as those from domestic and semi-wild animals treated with antibiotics to enhance growth, has been scanty. Such research is important as the use of antibiotics may alter the composition of bones, and thus their potential as a green adsorbent to remove fluoride may be impaired. Furthermore, little attempt has been made so far to package char bones for easy application domestically, particularly in rural communities. SIGNIFICANCE: • Contamination of water by fluoride is a major problem globally. • Various techniques and materials have been employed for water defluoridation, including the use of bone char, which has several advantages. • Bone char prepared from bones of animals in the wild and those from domestic and semi-wild animals treated with antibiotics to enhance growth should be further investigated. • Cheaper and less elaborate processes and packaging are required to scale down the use of bone char at domestic level.

South Africa has one of the largest Cr-related industries in the world and generates large amounts of Cr-containing smelter dusts. It is normal practice to scrub Cr from the furnace off-gas in water, and to recover the Cr by adsorption, followed by recycling of the loaded adsorbent into the furnace. A study was conducted to find a low-cost adsorbent that is capable of removing sufficient Cr from the solutions generated by scrubbing. The test work focused on the evaluation of different clay minerals (attapulgite, bentonite, and kaolinite) as adsorbents for Cr. Cr(VI) could only be adsorbed after prereduction with e.g. ascorbic acid (ASA). An 80% removal of Cr(VI) could be achieved from a solution containing 20 mg/L Cr using bentonite clay after reduction with ASA. Attapulgite and kaolinite adsorbed less than 55% Cr after reduction with ASA. Both ASA and ferrous salts were found to be suitable reducing agents. The use of acid mine drainage (AMD) was also investigated as a low-cost alternative reducing agent, as AMD usually contains iron. The Cr(VI) reduction potential of the AMD was determined by redox titration against a solution containing 50 mg/L Cr(VI). Studies show that AMD can potentially be used as a reducing agent in a Cr removal process if it is available on site.

The extensive consumption of tetracyclines (TCs) has gained attention due to their toxic effect. The current study reports the synthesis and characterization of magnetic chitosan-polypyrrole (Cs-PPy-Fe3O4) composite, which was then used for the adsorption of TCs from aqueous solutions. The synthesized adsorbent had a surface area, pore volume, and pore size diameter of 129 m² g-1, 0.32 cm³ g-1, and 9.9 nm, respectively. Furthermore, the adsorbent had an elemental composition of C (53.6%), O (18.0%), N (12.4%), Fe (12.4%) and O (18.0%). Box-Behnken design (BBD) was used to investigate the effects of various parameters affecting the adsorption of TCs onto Cs-PPy-Fe3O4 composite. The results displayed that the sorption of the TCs onto Cs-PPy-Fe3O4 composite followed pseudo-first-order and best fitted the Langmuir isotherm model with adsorption capacities of 112, 95, 94, and 93 mg g-1 for oxytetracycline, tetracycline, chlortetracycline, and doxycycline, respectively. Thermodynamic studies revealed that the adsorption of the analytes onto the Cs-PPy-Fe3O4 composite was physical with exothermic and increasing entropy. Furthermore, as the eluting solvent, the adsorbent could be regenerated using methanol and 0.01 oxalic acid (20:80 v/v). Therefore, the Cs-PPy-Fe3O4 composite could be a promising adsorbent for the simultaneous removal of TCs in water.