Nanoclays and mineral derivates applied to pesticide water remediation.

Although pesticides are vital in agroecosystems to control pests, their indiscriminate use generates innumerable environmental problems daily. Groundwater and surface water networks are the most affected environmental matrices. Since these water basins are mainly used to obtain water for human consumption, it is a challenge to find solutions to pesticide contamination. For these reasons, development of efficient and sustainable remedial technologies is key. Based on their unique properties including high surface area, recyclability, environmental friendliness, tunable surface chemistry and low cost, nanoclays and derived minerals emerged as effective adsorbents towards environmental remediation of pesticides. This study provides a comprehensive review of the use of nanoclays and mineral derivatives as adsorbents for pesticides in water. For this purpose, the characteristics of existing pesticides and general aspects of the relevant clays and minerals are discussed. Furthermore, the study provides insightful discussion on the potential application of nanoclays and their derivatives toward the mitigation of pesticide pollution in the environment. Finally, the outlook and future prospects on nanoclay implications and their environmental implementation are elucidated.

Removal efficiency of As(III) from aqueous solutions using natural and Fe(III) modified bentonites.

Contamination of water with arsenic is a major global health problem. The use of adsorbent materials for the removal of As from aqueous systems is a plausible solution to this problem. In this work, the use of commercial bentonites (purified and modified with iron (III)) for the removal of As from water was studied. The samples were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier Transformed Infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and nitrogen adsorption/desorption isotherms to determine their physicochemical properties. The arsenic removal capacities of adsorbent materials were studied from 1 mg/L solutions of As (III) using the colorimetric technique of molybdenum blue. High adsorption capacity (0.33 mg/g) of As (III) was obtained in aqueous systems after 1 h of treatment with unmodified bentonite. The incorporation of iron improved the removal performance in short times. The obtained results could be the starting point for the development of a low-cost filtration system that contributes to solve the problem of arsenic in water.

Amphiphilic tricationic Zn(II)phthalocyanine provides effective photodynamic action to eradicate broad-spectrum microorganisms.

A novel tricationic Zn(II)phthalocyanine derivative, (NCH3)3ZnPc3+, was synthesized by ring expansion reaction of boron(III) [2,9(10),16(17)-trinitrosubphthalocyaninato]chloride. First, the reaction of this subphthalocyanine with 2,3-naphthalenedicarbonitrile and Zn(CH3COO)2 catalyzed by 8-diazabicyclo[5.4.0]undec-7-ene was used to obtain the A3B-type nitrophthalocyanine. After reduction of nitro groups with Na2S and exhaustive methylation of amino groups, (NCH3)3ZnPc3+ was formed in good yields. In addition, the tetracationic analog (NCH3)4ZnPc4+ was synthesized to compare their properties. The absorption and fluorescence spectra showed the Q-bands and the red emission, respectively, which are characteristic of the Zn(II)phthalocyanine derivatives in N,N-dimethylformamide. Furthermore, photodynamic activity sensitized by these compounds was studied in the presence of different molecular probes to sense the formation of reactive oxygen species. (NCH3)3ZnPc3+ efficiently produced singlet molecular oxygen and also it sensitized the formation of superoxide anion radical in the presence of NADH, while the photodynamic activity of (NCH3)4ZnPc4+ was very poor, possibly due to the partial formation of aggregates. Furthermore, the decomposition of L-tryptophan induced by (NCH3)3ZnPc3+ was mainly mediated by a type II mechanism. Antimicrobial photodynamic inactivation sensitized by these phthalocyanines was evaluated in Staphylococcus aureus, Escherichia coli, and Candida albicans, as representative microbial cells. In cell suspensions, (NCH3)3ZnPc3+ was rapidly bound to microbial cells, showing bioimages with red fluorescence emission. After 5 min of irradiation with visible light, (NCH3)3ZnPc3+ was able to completely eliminate S. aureus, E. coli and C. albicans, using 1.0, 2.5 and 5.0 µM phthalocyanine, respectively. In contrast, a low photoinactivation activity was found with (NCH3)4ZnPc4+ as a photosensitizer. Therefore, the amphiphilic tricationic phthalocyanine (NCH3)3ZnPc3+ is a promising photosensitizing structure for application as a broad-spectrum antimicrobial phototherapeutic agent.

Potentiation Effect of Iodine Species on the Antimicrobial Capability of Surfaces Coated with Electroactive Phthalocyanines.

The spreading of different infections can occur through direct contact with glass surfaces in commonly used areas. Incorporating the use of alternative therapies in these materials seems essential to reduce and also avoid bacterial resistance. In this work, the capability to kill microbes of glass surfaces coated with two electroactive metalated phthalocyanines (ZnPc-EDOT and CuPc-EDOT) is assessed. The results show that both of these materials are capable of producing reactive oxygen species; however, the polymer with Zn(II) (ZnPc-PEDOT) has a singlet oxygen quantum yield 8-fold higher than that of the Cu(II) containing analogue. This was reflected in the in vitro experiments where the effectiveness of the surfaces was tested in bacterial suspensions, monitoring single microbe inactivation upon attachment to the polymers, and eliminating mature biofilms. Furthermore, we evaluated the use of an inorganic salt (KI) to potentiate the photodynamic inactivation mediated by an electropolymerized surface. The addition of the salt improved the efficiency of phototherapy at least two times for both polymers; nevertheless, the material coated with ZnPc-PEDOT was the only one capable of eliminating >99.98% of the initial microbes loading under different circumstances.

Silica nanoparticles embedded with water insoluble phthalocyanines for the photoinactivation of microorganisms.

Silica nanoparticles (SiNPs) embedded with Zn(II) 2,9,16,23-tetrakis(methoxy)phthalocyanine (SiNPZnPcOCH3), Zn(II) 2,9,16,23-tetrakis(4-pyridyloxy) phthalocyanine (SiNPZnPcOPy) and Zn(II) 2,9,16,23-tetrakis(t-butyl) phthalocyanine (SiNPZnPctBu) were synthesized in the nonpolar core of AOT/1-butanol/water micelles using triethoxyvinylsilane and 3-aminopropyltriethoxysilane. These SiNPs-Pc presented an average diameter of about 20-25 nm. UV-vis absorption spectra presented the characteristic Soret and Q bands of phthalocyanines embedded into the nanoparticles. Moreover, red fluorescence emission of SiNPs bearing phthalocyanines was detected in water. The SiNPs-Pc produced the photodecomposition of 2,2'-(anthracene-9,10-diyl)bis(methylmalonic acid), which was used to sense the singlet molecular oxygen O2(1Δg) generation in aqueous medium. Also, the formation of superoxide anion radical was detected by nitro blue tetrazolium reduction in the presence of NADH. Photoinactivation of microorganisms was investigated in Staphylococcus aureus and Candida albicans. In vitro experiments showed that photosensitized inactivation induced by SiNPZnPcOCH3 and SiNPZnPctBu improved with an increase of irradiation times. After 30 min irradiation, over 7 log reduction was found for S. aureus. Also, these SiNPs-Pc produced a decrease of 2.5 log in C. albicans after 60 min irradiation. In both cases, a lower photoinactivation activity was found for SiNPZnPcOPy. Studies of photodynamic action mechanism showed that the photokilling of microbial cells was protected in the presence of sodium azide and diazabicyclo[2.2.2]octane. Also, a reduction on the cell photodamage was found with the addition of D-mannitol. Therefore, the photodynamic activity sensitized by SiNPZnPcOCH3 and SiNPZnPctBu in microbial cells was mediated by a contribution of both type I and type II photooxidative mechanisms. Thus, silica nanoparticles are interesting materials to vehicle ZnPcOCH3 and ZnPctBu in aqueous media to photoeradicate microorganisms.