The environmental applications of activated carbon/zeolite composite materials
Introduction
Throughout the past several decades, the exponential population and social civilization expansion, change affluent lifestyles and resources use, and continuing progress of the industries and technologies has been accompanied by a sharp globalization and metropolitan growth [1]. Hitherto, the deleterious disruptions of the immense industrial effluents seepage, essentially endorsed by the miscellaneous emissions of metal finishing, coal mining, mineral extracting, oil refining, food processing, pharmaceuticals, cosmetics, coffee pulping, dye manufacturing, vehicle emissions, pulp tanneries and electroplating distilleries, chiefly in the form of carbon dioxide, hydrogen, methane, hydrogen sulphite, ammonia, volatile organic compounds or heavy metals, have intensified threatening deteriorations towards the public health and food chain interference [2].
In the formal practice, it was a convenient way to dispose industrial effluents by uncontrolled tipping or dumping, an operation in which waste is spread or released to fill in low economic value open dumps on selected pieces of land (inundated swampland, abandoned sand mines and quarries) or directly into the atmosphere, without taking care of the surrounding environment, nor considering any precautions to compact, cover and prohibit the infiltration of contaminants into the underlying waterways [3]. Lately, the enforcement of environmental rules and regulations concerning the monitoring of pollution from industrial effluent streams by regulatory agencies is becoming more stringent and restrictive, inevitably affecting the design, planning, and operation of the waste processing plants. This has inspired a growing research interest in establishing a leading selective, reliable and durable alternative for judicious treatment of the heavily polluted entities.
In particular, the potentiality of the zeolite-mediated heterogeneous processes, exclusively featured by the high reactivity for complete elimination of recalcitrant pollutants and environmental remediation, has become the focus of intense interest, mainly hinges on its synergetic adsorption strength, controllable pore structure, excellent chemical stability, and superior ability for removing a broad range of organic and inorganic pollutants dissolved in aqueous media, even from gaseous environment [4], [5]. Despite its prolific use in pollutants purification, the biggest barrier of its wide scale application is the cost-prohibitive reaction medium associated with catalyst suspensions, leaching, settling, dissolution, floatation and essentiality for eventual separation and recovery of the fine particles during its post treatment process.
Realizing the complications, a growing exploration to immobilize, anchor, embed or disperse zeolite onto an inert, high surface area, well developed porosity, and suitable supporting matrix (glass, ceramics, polymers silica, alumina or activated carbon) in different arrangements, which reacts as a noble sink promoting energy and interfacial charge transfer within the particle pertaining its catalytic efficiency has been exerted [6], [7]. With the aforementioned, this review attempts to postulate an initial platform in describing the origin, distinct physiochemical properties, development and potential application of the zeolite/activated carbon composite materials. The present work is aimed at providing a concise and up to date picture of zeolite and advancement of zeolite/activated carbon composite catalysts. The comprehensive literature together with the challenges and future perspectives has been highlighted and outlined, to familiarize the knowledge deficiencies regarding the evolution of zeolite/activated carbon composites technology.
Section snippets
The origin, classification, critical properties and background study of the zeolite compounds
In general, zeolite is defined as a diverse group of inorganic, alkaline and hydrated crystalline aluminum-silicates, tetrahedral connecting neighboring corners by sharing their oxygen atoms (O-sites), forming a regular spatial arrangement of uniform cages, cavities or channels of molecular dimensions (typically in the 4 to 15 Ǻ range) (Fig. 1) [8], [9]. Its internal skeleton is built from a three-dimensional framework of 4-valent TO4 unit cells (T = Si, Al, B, Ga, Ge, Fe, P and Co) accommodating
Inherent drawbacks of the zeolite accommodated processes and advancement of the activated carbon/zeolite composite materials
Within the last few years, intensive wide spread contamination of atmosphere and surface water related to adverse industrial operations has attested a fastidious concern for many environmentalists. A developing research by the invention of a broad array of treatment technologies (precipitation, coagulation–flocculation, sedimentation, flotation, filtration, membrane processes, electrochemical techniques, biological process, chemical reactions, adsorption and ion exchange) [40], [41], [42], [43]
Emergence of activated carbon/zeolite composites material in the wastewater treatment industries
Since recent era, water pollution control has prevailed to be the most thrust area and arduous task abroad the nations. Limited availability of high-quality potable water supplies is forcing the implementation of in-process water saving measures and advanced treatment processes for water recycling and scavenging of the industrial effluents. With the escalating of the imperative manufacturing and giant processing industries, adsorption process, a surface phenomenon by which a multi-components
Prevalence of activated carbon/zeolite composites for gas purification
Water scarcity and air pollution rank equal to climate change as the most intricate environmental turmoil for the 21st century. To date, the percolation of industrial gas effluents into the aquifer systems and atmosphere, specifically governed by the precipitation of rain water, volatilization (diffuse-source inputs) or accidental spillage, constitutes an accumulative, persistent and detrimental terrorist towards the survival of aquatic compartments, flora, fauna and environmental matrix (water
Utilization of activated carbon/zeolite composites material in the hydrogen storage chemistry
For the last few centuries, tremendous efforts devoted to formulate a renewable, environment-friendly and sustainable alternative energy in fulfilling the compelling needs of the dwindling oil reserves (reduce the prodigious dependency on fossil fuels), and simultaneously resolving the global warming and green house emissions, have received stern encourages and considerations worldwide. Among the candidates, hydrogen gas, a tasteless, colorless, odorless and nontoxic energy molecule, holds a
Major challenges and future prospects
The world is currently facing the worst environmental crisis in its entire history. For the past two decades, the enthusiasm of huge waste production and the terminology of industrial effluents exposure have been one of the rapidly advancing dilemmas, which have attracted greatest public considerations and spectacular attention towards the recovery of contamination resources [84], [85], [86]. Arising from the steep development of the world's giant manufacturing factories and transitions to the
Conclusion
Over the years, the world's industrialization and globalization growth are gradually expanding, driving towards the overwhelming waste generation. Predictions for the next 20 years indicate an embraced failing of industrial processing sectors and subsequently in huge waste generation. Today, the growing discrepancy and limited success of remediation in field applications have raised apprehensions over the use of zeolite/activated carbon composite materials as a measure to environmental pollution
Acknowledgement
The authors acknowledge the financial support provided by Universiti Sains Malaysia under the Research University (RU) Scheme (Project No. 1001/PJKIMIA/814072) and RU-PRGS grant scheme (Project No. 8043030).
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