Compounds based on iron mining tailing dams and activated carbon from macauba palm for removal of emerging contaminants and phosphate from aqueous systems.

In this work, an iron-rich residue, which is widely obtained as a by-product in the iron mining industry, and macauba endocarp, waste from the extraction of vegetable oil for the production of biofuels, were used in the preparation of different composites based on iron and carbon. The composites were obtained by manual grinding of the calcined iron residue and activated carbon prepared by the macauba endocarp followed by thermal treatment under nitrogen atmosphere. The effect of the thermal treatment was analyzed by Mössbauer spectroscopy and X-ray diffraction and showed that the increase in the treatment temperature promoted the formation of different reduced iron phases in the final composite, such as Fe3O4, FeO, and Fe0. These composites were used in a combined adsorption/oxidation process through photocatalysis to remove up to 93% of amoxicillin from aqueous phase. The formation of possible reaction intermediates was monitored by electrospray ionization mass spectrometry (ESI-MS) and a mechanism of amoxicillin degradation was proposed. Afterward, the Fe/C composites were conducted to evaluate the impact of several parameters on phosphate adsorption processes and showed a maximum adsorption capacity of 40.3 mg g-1. The adsorption capacity obtained for all the materials were greater than those found in the literature.

Influence of the surface modification of granular-activated carbon synthesized from macauba on heavy metal sorption.

Adsorption on activated carbon is a promising technique for the treatment of low-concentration heavy metal pollutants in water with high efficiency and simple operation. However, commercial-activated carbon is often associated with high costs. Therefore, much attention has been given to activated carbon derived from low-cost agricultural and residual biomass. In this work, adsorption of Zn, Cd, and Pb ions in aqueous solutions was conducted using granular-activated carbon obtained from macauba palm, biomass waste of biofuel production, after surface modification using different methods. The adsorbents were obtained in granular form which facilitates all steps of the use, recovery, and reuse of the material, differently from the powdered-activated carbon normally used. The materials were characterized by using XPS, elemental analysis, N2 sorption (BET method), and zeta potential measurements. Such techniques allowed observation of the functionalization of the carbon surface. The materials presented high adsorption capacities when compared to other works in the literature, with a capacity of approximately 7.69, 8.42, and 1.63 mmol g-1 for Zn2+, Cd2+, and Pb2+, respectively. In addition, the materials showed a high capacity to be reused, removing 75% of Pb and 99% of both Cd and Zn after 4 cycles.

Amoxicillin photodegradation under visible light catalyzed by metal-free carbon nitride: An investigation of the influence of the structural defects.

Herein, the structural defects of metal-free polymeric carbon nitrides were controlled by making use of different precursors in their syntheses, i.e. melamine (CN-M) and thiourea (CN-T), as well as a 1:1 mixture of them (CN-1M:1 T). By controlling the structural defects, the electronic, morphological and chemical properties were modified. Additionally, the activities of synthesized PCNs were evaluated for amoxicillin photodegradation under visible light irradiation (16 mW cm-2). The results of photocatalytic tests showed that CN-T material has better efficiency (100 % removal within 48 h), which is directly related to the greater number of defects present in its structure with consequent improvement of electron-hole pairs separation efficiency. The CN-T material showed excellent stability with only 13 % decrease in its photocatalytic activity after the third cycle. A mechanism for amoxicillin degradation by CN-T was proposed based on the ESI-MS and the in situ EPR allied with spin trapping method investigations.

Efficient activation of peroxymonosulfate by composites containing iron mining waste and graphitic carbon nitride for the degradation of acetaminophen.

In this work, the potential to use an iron mining waste (IW), rich in α-Fe2O3 and α-FeOOH, for the development of composites based on graphitic carbon nitride (CN) is demonstrated. These materials were synthesized through a simple thermal treatment at 550 °C of a mixture containing melamine and different IW mass percentages, giving rise to the catalysts xIWCN (where x is related to the initial mass percentage of IW). The iron phases of the precursor were partially transformed throughout the formation of the composites, in such a way that a mixture of α-Fe2O3 and γ-Fe2O3 was observed in their final composition. Furthermore, structural defects were produced in the carbonaceous matrix of the materials, causing the fragmentation of g-C3N4 and an increase of surface area. The catalytic activities of these composites were evaluated in reactions of peroxymonosulfate activation for the degradation of paracetamol. Among these materials, the composite 20IWCN showed the best catalytic activity, being able to degrade almost 90 % of the total paracetamol in only 20 min of reaction. This catalyst also demonstrated high chemical stability, being successfully utilized in five consecutive reaction cycles, with negligible iron leaching.

Emerging contaminants removal by granular activated carbon obtained from residual Macauba biomass.

The removal of emergent contaminants via adsorption on granular activated carbon, prepared from Macauba palm, has been studied, contributing to the recovery of the residual biomass, endocarp, obtained in the Macauba palm oil extraction process. The material was characterized by different techniques, such as Raman spectroscopy, thermal analysis, adsorption/desorption of N2, zeta potential, and scanning electron microscopy. The N2 adsorption studies showed that the material presents wide micropores and narrow mesopores, and has a surface area of 907.0 m2 g-1. Its maximum adsorption capacity towards the three main emerging contaminants (bisphenol A, ethinylestradiol, and amoxicillin) is much higher than that obtained with benchmark adsorbents (0.148, 0.104, and 0.072 mmol g-1, respectively). The influence of temperature and pH on the adsorption was also analyzed, allowing an improved description of the adsorption mechanism and showing very promising results.