Rational Design of Mesoporous Adsorbents for the Removal of Organic Pollutants from Water

Environmental pollution from various sources has become an increasing problem over the last several decades. One of the major global issues is the pollution of water. Water is a vital resource for all known forms of life and a necessity for the sustainability of earth's ecosystems. Water availability is affected by pollution caused by intensive agriculture, industrial production, mining and untreated urban runoff and wastewater. This pollution creates environmental and health risks [1]. The availability and access to pure water as a natural resource are therefore crucial for human health, agriculture, industry and natural ecosystems [2]. Organic pollutants are an important group of hazardous compounds contaminating water [3]. Efficient techniques for the removal of organic compounds from water have drawn significant interest. A number of methods such as adsorption, coagulation, filtration with coagulation, precipitation, ozonation, reverse osmosis and advanced oxidation processes have been used for the removal of organic pollutants from polluted water and wastewater. Most of these methods have been found to be limited, since they often involve high capital and operational costs. Among the possible techniques for water treatments, adsorption shows potential as one of the most efficient methods because of its simple design and low initial cost. [4]. Activated carbon (AC) is the most widely used commercial adsorbent to remove organic pollutants from wastewater due to its porous structure and high specific surface area [5]. However, AC is less suitable for the adsorption of pollutants with larger molecular size (e.g. bulky molecules or macromolecules). The inherent micropores (< 2 nm) are less accessible or even unable to host these large molecules leading to lower adsorption capacities. Mesoporous adsorbents on the other hand are materials with a pore size between 2 and 50 nm. These larger pore sizes will be advantageous in the adsorption of larger molecules. Interesting materials are mesoporous carbons, originally synthesized via a hard template route, in which a mesoporous silica is used as a template. This template was filled with carbon precursor which is polymerized in the pores. After template removal, porosity is created [6]. A more recently developed soft template method uses the interaction of carbon precursors with a micelle-forming surfactant to synthesize mesoporous carbons. A treatment at high temperatures in an inert atmosphere removes the surfactant, creating porosity in the mesoporous carbon [7]. This method involves less synthesis steps and does not require a hard template, which needs to be removed with dangerous HF. The versatility in reaction conditions of soft templated mesoporous carbons can lead to a broad range of carbons in which the material properties can be tailored to specific needs. Another novel mesoporous material gaining interest as adsorbent is hexagonal boron nitride which is known for its chemical and thermal stability. It has a similar chemical structure to graphite which allows the successful adsorption of organic pollutants. With the introduction of porosity into this material, a chemical and thermal stable efficient adsorbent could be obtained. In summary, the need for a cleaner environment and efficient ways to remove pollutants from water requires the development of better adsorbents. In order to address new challenges, tailor-made adsorbents need to be developed to meet specific requirements. A fundamental understanding in the design of new mesoporous materials with control over material properties, e.g. specific surface area, pore volume, pore size or surface chemistry is crucial to efficiently remove organic pollutants from water.

http://ift.tt/2s5vXui