A review on the adsorption of heavy metals by clay minerals, with special focus on the past decade

PROMETHEE: A comprehensive literature review on methodologies and applications

The use of zero-valent iron for groundwater remediation and wastewater treatment: a review.

In the last few decades, pharmaceuticals, credited with saving millions of lives, have emerged as a new class of environmental contaminant. These compounds can have both chronic and acute harmful effects on natural flora and fauna. The presence of pharmaceutical contaminants in ground waters, surface waters (lakes, rivers, and streams), sea water, wastewater treatment plants (influents and effluents), soils, and sludges has been well doccumented. A range of methods including oxidation, photolysis, UV-degradation, nanofiltration, reverse osmosis, and adsorption has been used for their remediation from aqueous systems. Many methods have been commercially limited by toxic sludge generation, incomplete removal, high capital and operating costs, and the need for skilled operating and maintenance personnel. Adsorption technologies are a low-cost alternative, easily used in developing countries where there is a dearth of advanced technologies, skilled personnel, and available capital, and adsorption appears to be the most broadly feasible pharmaceutical removal method. Adsorption remediation methods are easily integrated with wastewater treatment plants (WWTPs). Herein, we have reviewed the literature (1990-2018) illustrating the rising environmental pharmaceutical contamination concerns as well as remediation efforts emphasizing adsorption.

Pharmaceuticals of Emerging Concern in Aquatic Systems: Chemistry, Occurrence, Effects, and Removal Methods.

It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field.

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Recent Advances in the Catalytic Oxidation of Volatile Organic Compounds: A Review Based on Pollutant Sorts and Sources.

Heterogeneous Fenton reactions have gained widespread attention in removing recalcitrant organic contaminants as the reaction between solid Fenton catalysts and H2O2 can generate highly reactive hydroxyl radicals (HO[rad]). However, several drawbacks, such as the low-speed generation of Fe(II), high consumption of H2O2, and acidic reaction conditions (generally at ˜ pH 3), are always the core issues that hamper the large-scale application of heterogeneous Fenton reactions in environmental remediation. Thus, a large number of studies have been devoted to tackling these drawbacks, and this paper intends to comprehensively review the developed strategies for enhancing heterogeneous Fenton reactivity, mainly over the last decade. Based on a comprehensive survey of previous studies, we categorize these strategies according to their reaction mechanisms. For example, introducing additional electrons (e.g., from external electric fields, electron-rich materials, semiconductors, plasmonic materials, or doped metals) to heterogeneous Fenton catalysts can accelerate the generation of Fe(II); the in situ generation of H2O2 can be achieved by combining ultrasound, electricity, semiconductors, and iron-based catalysts in the system; and controlling the specific morphologies and exposed facets of heterogeneous Fenton catalysts can greatly promote the decomposition of H2O2. In addition, we briefly introduce some recent novel heterogeneous Fenton-like reactions that are of particular interest, including constructing dual reaction centers (i.e., the electron-poor center and the electron-rich center) and synthesizing single-atom catalysis-based heterogeneous Fenton-like catalysts. Moreover, this review article analyzes and compares the merits of each strategy for enhancing heterogeneous Fenton/Fenton-like reactions. We believe this review can motivate the construction of novel and efficient heterogeneous Fenton/Fenton-like systems and help readers choose proper Fenton/Fenton-like reaction systems for industrial applications.

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Strategies for Enhancing the Heterogeneous Fenton Catalytic Reactivity: A review

Adsorbents based on montmorillonite for contaminant removal from water: A review

X-ray diffraction has been used to study the changes in the surface properties of a montmorillonitic clay through the changes in the basal spacings of montmorillonite (SWy-2) and surfactant-intercalated organo-clays.
Variation in the d-spacing was found to be a step-function of the surfactant concentration. High resolution thermogravimetric analysis (HRTG) was used to study the thermal decomposition surfactant modified SWy-2-MMTs modified with the surfactant octadecyltrimethylammonium bromide. High resolution thermogravimetry shows the decomposition takes place in 4 steps. A mass loss step is observed at room temperature and is attributed to dehydration of adsorption water. A second mass loss step is observed over the 87.9 to 135.5 degrees Celsius temperature range and is also attributed to dehydration of water hydrating metal cations such as Na+ . The third mass loss occurs from 178.9 to 384.5 degrees Celsius and is assigned to a loss of surfactant. The fourth mass loss step is ascribed to the loss of OH units through dehydroxylation over the 556.01 to 636.35 degrees Celsius temperature range.

Structure of organoclays—an X-ray diffraction and thermogravimetric analysis study

Changes in the morphology of organoclays with HDTMA+ surfactant loading

Surfaces of a Wyoming SWy-2 sodium montmorillonite were modified using microwave radiation through intercalation with the cationic surfactants octadecyltrimethylammonium bromide, dimethyldioctadecylammonium bromide, and methyltrioctadecylammonium bromide by an ion exchange mechanism. Changes in the surfaces and structure were characterized using X-ray diffraction (XRD), thermal analysis (TG) and infrared (IR) spectroscopy. Different configurations of surfactants within montmorillonite interlayer are proposed based on d(001) basal spacings. A range of surfactant molecular environments within the surface-modified montmorillonite are proposed based upon their thermal decomposition. IR spectroscopy using a smart endurance single bounce diamond attenuated total reflection (ATR) cell has been used to study the changes in the spectra of CH asymmetric and symmetric stretching modes of the surfactants to provide more information of the surfactant molecular configurations.

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Modification of the surfaces of Wyoming montmorillonite by the cationic surfactants alkyl trimethyl, dialkyl dimethyl, and trialkyl methyl ammonium bromides.

Yunfei Xi

Papers

Strategies for Enhancing the Heterogeneous Fenton Catalytic Reactivity: A review

Adsorbents based on montmorillonite for contaminant removal from water: A review

Structure of organoclays—an X-ray diffraction and thermogravimetric analysis study

Changes in the morphology of organoclays with HDTMA+ surfactant loading

Modification of the surfaces of Wyoming montmorillonite by the cationic surfactants alkyl trimethyl, dialkyl dimethyl, and trialkyl methyl ammonium bromides.