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Waste of Mytella falcata shell was used as low-cost adsorbent to remove the biocide Basic Green 4 (BG4) from water. Shells were collected form trash nearby the lagoon were Mytella falcata is fished. After clean, dry and crushed, the powder was characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), and X-ray dispersive energy spectroscopy (EDS). Both kinetic and equilibrium adsorption tests are carried out. Adsorbent regenerability was tested during adsorption/desorption cycles, using a UV photo-regeneration process. The maximum adsorption capacity reached 539.24 mg.g-1 (60 °C), which was higher than those retrieved for other materials with similar origin. The kinetic results indicated that the process followed pseudo-second order model. Equilibrium data indicate an increase in BG4 adsorption capacity with temperature and Sips model had better fit for all the investigated temperatures (30, 40, 50 and 60 °C). The regeneration/reuse test indicated that the adsorbent is able to assure a BG4 removal above 70 % during five adsorption/desorption cycles evaluated. Thermodynamic parameters suggested that adsorption is spontaneous, endothermal, governed by chemisorption and with structural changes in the solid surface upon adsorption.

This work deals with the use of Mytella falcata shells (a bivalve mollusk) as innovative biosorbent for the removal of rifampicin antibiotic from water. The material is alternatively tested as raw or after either pyrolysis or calcination, in order to improve its adsorption capacity. The calcination temperature (700 °C) was determined from the thermogravimetric analysis (TGA) of the raw shell. Preliminary adsorption tests allow individuating the calcined sample as the most performing. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and X-ray-dispersive energy spectroscopy (EDS) are used for characterization of the adsorbent. They showed the presence of residual CaCO3, mainly in the form of aragonite and calcite, and a porous structure with heterogeneous surface characterized by rounded particles. Kinetic tests showed fast adsorption phenomena, which were completed in 30−45 min. They present the best fit with pseudo-first order model and the equilibrium adsorption capacity obtained in the different tests (3.05, 4.58 e 7.00 mg.g−1) were satisfactorily predicted. Equilibrium data show that rifampicin adsorption capacity is almost independent on temperature, probably for the simultaneous increase in water desorption associated with the increase in temperature. The isotherms show a Redlich-Peterson model behavior, indicating a multilayer adsorption. The analysis of thermodynamic parameters shows that adsorption is spontaneous and slightly endothermic. Further experimental tests to simulate different water matrix indicate that a high ionic strength can increase the adsorption of rifampicin on the selected adsorbent. Finally, adsorbent regeneration by sonication shows a significant decrease in the performances after 5 adsorption/desorption cycles.

Mytella falcata shells were used as adsorbent to remove 17-α-methyltestosterone from water. Preliminary tests were carried out to evaluate the affinity of the mollusk shells in their natural, pyrolyzed and calcined form in relation to the hormone. Pyrolyzed material showed the best performance. The influence of the solution pH and the adsorbent load were also evaluated. The material was characterized by thermogravimetry, Fourier Transform Infrared Spectroscopy, X-ray diffraction, Point of Zero charge and Scanning Electron Microscopy. Adsorption assays reveals better kinetic fit for pseudo second order, with mechanism follow diffusion in bulk and intraparticle, while the Sips model presented a better fit to the equilibrium experimental data. The maximum adsorption capacity reached 0.778 mg.g−1 at 50 oC. The process takes place in an exothermic way, being governed by forces from chemical nature, as indicated by the thermodynamic parameters. The artificial neural network with one hidden layer and three neurons showed up a promising tool in predicting equilibrium relationships of the adsorptive process. The neural model was equivalent to the isotherms models found in literature used to predict the adsorption kinetics and adsorption equilibrium. In terms of removal percentage, the adsorbent showed promising results achieving 70% for ultrapure water. On the other hand, when real water matrices were applied, the lower removal occurred with lagoon water (30%), and the highest removal was achieved using mineral water (80%), indicating this waste material as good alternative for the removal of endocrine disruptors from different types of water.

A Layered Double Hydroxides (LDH) with Mg and Al composite (MgAl/LDH-biochar) was synthesised by the co-precipitation method, using bovine bone activated carbon as support structure for the LDH particles. The adsorbent was applied for diclofenac sodium (DS) removal from synthetic water. Batch experiments provided a DS removal of almost 80 % under optimized conditions. The performances of the MgAl/LDH-biochar composite (i.e. adsorption capacity as much as 5.96 mg/g) result significantly better when compared to the raw biochar (2.35 mg/g) at first 15 min. Despites the equilibrium data provided good adjustments for all tested models, Redlich-Peterson model showed the highest values of R2 and lower values of average relative error (ARE) and Akaike’s information criterion (AIC). The kinetic data of DS adsorption was best represented by the pseudo-second order model. The regenerability of MgAl/LDH-biochar was also evaluated through six adsorption/desorption cycles using either methanol or sodium chloride (0.5 mol/L) as desorbing agents, showing that the material can be reused until the third cycle maintaining a good adsorption capacity. The thermodynamic studies suggested that the adsorption process was spontaneous and exothermic, since the adsorption capacity decreased when the temperature increased. Finally, for a deeper insight in the DS adsorption mechanism, monolayer model formulated via statistical physics was adopted to describe the adsorption geometry of this relvant water pollutant and also to further characterize the interactions between DS and the tested adsorbent.

In this work, the potential of ouricuri ( Syagrus coronata ) fiber as a novel biosorbent to remove methylene blue (MB) from aqueous solutions was investigated. The fiber was prepared and characterized according to the fundamental features for adsorption. A 2 3 experimental design was used to evaluate the effects of adsorbent dosage ( M ), fiber diameter ( D ) and agitation ( A ) on the adsorption capacity. In the more adequate conditions, kinetic and equilibrium studies were performed. The experimental design results showed that M = 10 g L −1 ), D = 0.595 mm and A = 200 rpm were the more adequate conditions for MB adsorption. Based on the kinetic study, it was found that the adsorption process was fast, being the equilibrium attained at about 5 minutes, with 90% of color removal. The isotherm was properly represented by the Sips model, and the maximum adsorption capacity was 31.7 mg g −1 . In brief, it was demonstrated that ouricuri fiber is an alternative biosorbent to remove MB from aqueous media, taking into account the process efficiency and economic viewpoint.