Glaydson S. dos Reis

Mesoporous Nb2O5/SiO2 material obtained by sol–gel method and applied as adsorbent of crystal violet dye

ABSTRACT In this work, SiO2/Nb2O5 (SiNb) material was prepared using sol–gel method and employed as adsorbent for removal of crystal violet dye (CV). The material was characterized using nitrogen adsorption–desorption isotherms, FTIR spectroscopy, pHpzc, and SEM-EDS. The analysis of N2 isotherms revealed the presence of micro- and mesopores in the SiNb sample with specific surface area as high as 747 m2 g−1. For the CV adsorption process, variations of several parameters such as of pH, temperature, contact time, and concentration of dye of the process were evaluated. The optimum initial pH of the CV dye solution was 7.0. The adsorption kinetic and equilibrium data for CV adsorption were suitably represented by the general-order and Liu models, respectively. The maximum adsorption capacity of the CV dye by SiNb was achieved at 303 K, which attained 116 mg g−1 at this temperaure. Dye effluents were simulated and used to check the applicability of the SiNb material for treatment of effluents – the material showed very good efficiency for decolorization of dye effluents.

Activated carbon from sewage sludge for removal of sodium diclofenac and nimesulide from aqueous solutions

Sludge based activated carbons (ACs) were used to remove selected pharmaceuticals such as diclofenac (DCF) and nimesulide (NM) from aqueous solutions. The powered sewage sludge was mixed with different proportions of ZnCl2. The mixture was pyrolyzed in a conventional oven using three different temperatures under inert atmosphere. Afterwards, in order to increase the specific surface area and uptake capacity the carbonized materials were acidified with 6mol L−1 HCl under reflux at 80 °C for 3 hours. The characterization of ACs was achieved by scanning electron microscopy, FTIR, TGA, hydrophobicity index by water, n-heptane vapor adsorption and nitrogen adsorption/desorption curves. The specific surface area (SBET) of adsorbents varied between 21.2 and 679.3m2g−1. According to the water and n-heptane analysis data all ACs had hydrophobic surface. Experimental variables such as pH, mass of adsorbent and temperature on the adsorption capacities were studied. The optimum pH, mass of adsorbent and temperature for adsorption of DCF and NM onto ACs were found to be 7.0 (DCF) and 10.0 (NM), 30mg and 25 °C, respectively. The kinetic adsorption was investigated using general-order, pseudo-first order and pseudo-second order kinetic models, while the general-order model described the adsorption process most suitably. The maximum amounts of DCF and NM adsorbed were 156.7 and 66.4mg g−1 for sample 1(500-15-0.5), respectively.

Activated Carbon from Sewage Sludge for Preconcentration of Copper

ABSTRACT Sewage sludge was pyrolyzed in an inert atmosphere at 550°C after chemical treatment with ZnCl2 or KOH using an organic precursor to inorganic weight ratio of 1:1. The materials were used as adsorbents for removal of Cu(II) from aqueous solution. The adsorbents were characterized using adsorption/desorption nitrogen isotherms, thermal analysis, scanning electron microscopy, and elemental analysis. The results showed that copper removal was linked to surface pH and compounds present on the surface of the adsorbent. The KOH-treated adsorbent had a smaller surface area (186 m2 g−1) than the ZnCl2-treated adsorbent (192 m2 g−1). However, the KOH-treated adsorbent provided more efficient removal of Cu(II). The performance of the KOH-treated adsorbent may be due to the presence of basic groups on the surface. The Liu isotherm model provided the best description of the equilibrium data: The maximum adsorption capacities at 298 K for KOH-treated, ZnCl2-treated, and untreated sewage sludge were 31.85, 19.79, and 3.513 mg g−1, respectively. The highest desorption was obtained using 1.50 mol L−1 of HNO3 as the eluent. The recoveries of Cu(II) loaded adsorbents were 98.9% for ZnCl2-treated and 95.5% for KOH-treated adsorbents.

Alternative treatments to improve the potential of rice husk as adsorbent for methylene blue

Alternative treatments, such as, NaOH, ultrasound assisted (UA) and supercritical CO2 (SCO2), were performed to improve the potential of rice husk as adsorbent to remove methylene blue (MB) from aqueous media. All the treatments improved the surface characteristics of rice husk, exposing its organic fraction and/or providing more adsorption sites. The Langmuir and Hill models were able to explain the MB adsorption for all adsorbents in all studied temperatures. The experimental and modeled parameters demonstrated that the MB adsorption was favored by the temperature increase and by the use of NaOH-rice husk. The maximum adsorption capacities for the MB solutions (ranging from 10 to 100 mg L-1), estimated from the Langmuir model at 328 K, were in the following order: NaOH rice-husk (65.0 mg g-1) > UA-rice husk (58.7 mg g-1) > SCO2-rice husk (56.4 mg g-1) > raw rice husk (52.2 mg g-1). The adsorption was a spontaneous, favorable and endothermic process. In general, this work demonstrated that NaOH, UA and SCO2 treatments are alternatives to improve the potential of rice husk as adsorbent.

Microwave-activated carbons from tucumã (Astrocaryum aculeatum) seed for efficient removal of 2-nitrophenol from aqueous solutions

ABSTRACT Activated carbons (ACs) prepared from tucumã seed (Astrocaryum aculeatum) were used for 2-nitrophenol removal from aqueous solutions. The ACs were characterized by elemental analysis, FTIR, N2 adsorption/desorption isotherms, TGA, hydrophobicity/hydrophilicity balance, and total of acidic and basic groups. The ACs showed to have hydrophilic surfaces and they presented high specific surface areas (up to 1318 m2 g−1). In batch optimization studies, maximum removal was obtained at pH 7, contact time of 30 min, adsorbent dosage 1.5 gL−1 and temperature of 50°C. The general-order kinetic model and Liu isotherm model best fit the kinetic and equilibrium adsorption data with a maximum adsorption capacity of 1382 mg g−1 at 50°C. Effect of temperature and thermodynamic studies revealed that the adsorption processes of 2-nitrophenol onto ACs are dependent on temperature and are exothermic and spontaneous, respectively. About the applicability of the ACs for treating simulated effluents, the tucumã seed-activated carbon showed an excellent outcome in the treatment of simulated effluents, evidencing its high efficiency for phenolic compound adsorption. Tucumã seed-ACs showed to be cost effective and highly efficient adsorbents for efficient removal of 2-nitrophenol from aqueous solutions.

Photocatalytic Studies of Tio2/Sio2 Nanocomposite Xerogels

The use of titania-silica materials in photocatalytic processes has been proposed as an alternative to the conventional TiO2 catalysts, in order to facilitate the separation of products after the reaction. However, despite the large number of research in this field, the mechanism governing the photocatalytic activity of the mixed TiO2/SiO2 oxides is not clear. Titania-Silica nanocomposite xerogels were prepared by sol-gel method. This work has been used to describe the synthesis and the photocatalytic properties of TiO2-SiO2 nanocomposite xerogel. The nanocomposite xerogels were prepared by keeping the molar ratio of TEOS:TTIP:MtOH:DIW at 1: 1:6:14 respectively and the catalysts used were HCl and NH4OH. After the preparation xerogels were characterized by FTIR, XRD, UV and LLS. All these techniques show the amorphous nature of Titania-silica xerogel.

Preparation of CTAB-functionalized aqai stalk and its efficient application as adsorbent for the removal of Direct Blue 15 and Direct Red 23 dyes from aqueous media

ABSTRACT In this work, a new adsorbent material based on the chemical modification of aqai stalk (AS) with hexadecyltrimethylammonium bromide (CTAB) was proposed, forming a new material called AS-CTAB. The characterization data from the AS-CTAB adsorbent indicated that the biomass was chemically modified by the surfactant. The prepared material was successfully used as an adsorbent for the removal of Direct Blue 15 (DB-15) and Direct Red 23 (DR-23) from aqueous solutions. For both dyes, adsorption followed the Avrami kinetic model. The kinetic data were better fitted using the nonlinear Avrami fractional model for both dyes. The contact time between the adsorbent and adsorbate was fixed at 180 and 30 min for DB-15 and DR-23, respectively. This remarkable difference of contact time between the dyes with AS-CTAB adsorbent was attributed to the difference in the physicochemical characteristics of the dyes such as size of the molecule, hydrophilic–lipophilic balance, and polar surface area (PA). The Liu isotherm model displayed Qmax of 394.2 and 454.9 mg g−1 for DB-15 and DR-23, respectively, at 45°C. Since the AS-CTAB is not a porous material, electrostatic interaction was the main mechanism involved in the adsorption process for both dyes. The thermodynamic adsorption reaction was shown to be a spontaneous and endothermic process. The AS-CTAB adsorbent was also tested in the treatment of synthetic dye effluents and presented a removal of up to 95.41% of a simulated effluent containing several dyes and high saline concentration.

SLUDGE-ACTIVATED CARBONS FOR COPPER REMOVAL FROM AQUEOUS SOLUTIONS

In this work, activated carbons (ACs) were prepared using Sewage sludge as starting material. The ACs were pyrolyzed in an inert atmosphere at 550 °C after independent chemical treatment with ZnCl2 or KOH with ratio of 1:1. The materials were used as adsorbents for removal of Cu(II) from aqueous solutions. The adsorbents were characterized using adsorption/desorption nitrogen isotherm, SEM (scanning electron microscopy). The results showed that copper removal could be linked to surface pH and compounds present on the surface of adsorbent. KOH-treated adsorbent has smaller surface area (186 m2 g-1) than ZnCl2-treated adsorbent (192 m2 g-1), however, KOH-treated adsorbent exhibited higher removal of Cu(II). The performance of KOH-treated adsorbent could be attributed to the presence of basic groups on the adsorbent surface. Liu isotherm model gave the best description of the equilibrium data. From the Liu isotherm, the maximum adsorption capacities at 298 K for KOH-treated, ZnCl2-treated and sewage sludge (without inorganic activation) adsorbents are 31.85, 19.79 and 3.513 mg g−1, respectively. The best desorption experiment was obtained using 1.50 mol L-1 of HNO3 as eluent. Recoveries of Cu(II) from Cu(II)-loaded adsorbents are 98.9% (ZnCl2-treated) and 95.5% (KOH-treated.