Management of typical VOCs in air with adsorbents: status and challenges

The serious harm of volatile organic compounds (VOCs) to the ecological environment and human health has attracted widespread attention worldwide. With economic growth and accelerated industrialization, the anthropogenic emissions of VOCs have continued to increase. The most crucial aspect is to choose the appropriate adsorbent, which is very important for the VOCs removal. The search for environmentally friendly VOCs treatment technologies is urgent. The adsorption method is one of the most promising VOCs emission reduction technologies with the advantages of high cost-effectiveness, simple operation, and low energy consumption. One of the most critical aspects is the selection of the appropriate adsorbent, which is very important for the removal of VOCs. This work provides an overview of the sources and hazards of VOCs, focusing on recent research advances in VOCs adsorption materials and the key factors controlling the VOCs adsorption process. A summary of the key challenges and opportunities for each adsorbent is also provided. The adsorption capacity for VOCs is enhanced by an abundant specific surface area; the most efficient adsorption process is achieved when the pore size is slightly larger than the molecular diameter of VOCs; the increase in the number of chemical functional groups contributes to the increase in adsorption capacity. In addition, methods of activation and surface modification to improve the adsorption capacity for VOCs are discussed to guide the design of more advanced adsorbents.

Adsorptive and photocatalytic degradation potential of porous polymeric materials for removal of pesticides, pharmaceuticals, and dyes-based emerging contaminants from water

Life on earth is dependent on clean water, which is crucial for survival. Water supplies are getting contaminated due to the growing human population and its associated industrialization, urbanization, and chemically improved agriculture. Currently, a large number of people struggle to find clean drinking water, a problem that is particularly serious in developing countries. To meet the enormous demand of clean water around the world, there is an urgent need of advanced technologies and materials that are affordable, easy to use, thermally efficient, portable, environmentally benign, and chemically durable. The physical, chemical and biological methods are used to eliminate insoluble materials and soluble pollutants from wastewater. In addition to cost, each treatment carries its limitations in terms of effectiveness, productivity, environmental effect, sludge generation, pre-treatment demands, operating difficulties, and the creation of potentially hazardous byproducts. To overcome the problems of traditional methods, porous polymers have distinguished themselves as practical and efficient materials for the treatment of wastewater because of their distinctive characteristics such as large surface area, chemical versatility, biodegradability, and biocompatibility. This study overviews improvement in manufacturing methods and the sustainable usage of porous polymers for wastewater treatment and explicitly discusses the efficiency of advanced porous polymeric materials for the removal of emerging pollutants viz. pesticides, dyes, and pharmaceuticals whereby adsorption and photocatalytic degradation are considered to be among the most promising methods for their effective removal. Porous polymers are considered excellent adsorbents for the mitigation of these pollutants as they are cost-effective and have greater porosities to facilitate penetration and adhesion of pollutants, thus enhance their adsorption functionality. Appropriately functionalized porous polymers can offer the potential to eliminate hazardous chemicals and making water useful for a variety of purposes thus, numerous types of porous polymers have been selected, discussed and compared especially in terms of their efficiencies against specific pollutants. The study also sheds light on numerous challenges faced by porous polymers in the removal of contaminants, their solutions and some associated toxicity issues.

Behaviors of sodium and calcium ions at the borosilicate glass–water interface: Gaining new insights through an ab initio molecular dynamics study

We study reactivity and leaching at the calcium sodium borosilicate (CNBS)–water interface by means of a Car–Parrinello ab initio molecular dynamics simulation over a simulation time of 100 ps. With an emphasis on the comparison between the behaviors of Ca2+ and Na+ cations at the CNBS glass–water interface, different mechanism events during the trajectory are revealed, discussed, and correlated with other density functional theory calculations. We show that Na+ ions can be released in solution, while Ca2+ cannot leave the surface of CNBS glass. This release is correlated with the vacancy energy of Ca2+ and Na+ cations. Here, we found that the CNBS structure with the Na+ cation vacancy is energetically more favorable than the structure with the Ca2+ cation vacancy. The calcium adsorption site has been shown to have a greater affinity for water than can be found in the case of the sodium site, demonstrating that affinity may not be considered a major factor controlling the release of cations from the glass to the solution.

Adsorption of Toluene and Water over Cationic-Exchanged Y Zeolites: A DFT Exploration

In this study, density functional theory (DFT) calculations have been performed to investigate the adsorption mechanisms of toluene and water onto various cationic forms of Y zeolite (LiY, NaY, KY, CsY, CuY and AgY). Our computational investigation revealed that toluene is mainly adsorbed via π-interactions on alkalis exchanged Y zeolites, where the adsorbed toluene moiety interacts with a single cation for all cases with the exception of CsY, where two cations can simultaneously contribute to the adsorption of the toluene, hence leading to the highest interaction observed among the series. Furthermore, we find that the interaction energies of toluene increase while moving down in the alkaline series where interaction energies are 87.8, 105.5, 97.8, and 114.4 kJ/mol for LiY, NaY, KY and CsY, respectively. For zeolites based on transition metals (CuY and AgY), our calculations reveal a different adsorption mode where only one cation interacts with toluene through two carbon atoms of the aromatic ring with interaction energies of 147.0 and 131.5 kJ/mol for CuY and AgY, respectively. More importantly, we show that water presents no inhibitory effect on the adsorption of toluene, where interaction energies of this latter were 10 kJ/mol (LiY) to 47 kJ/mol (CsY) higher than those of water. Our results point out that LiY would be less efficient for the toluene/water separation while CuY, AgY and CsY would be the ideal candidates for this application.

Application of adsorption process for effective removal of emerging contaminants from water and wastewater

Emerging pollutants in the marine ecosystem, as well as their possible impact on live species, have become a rising cause of worry. A traditional wastewater treatment plants alone are not successful in eliminating such massive contaminant groups and therefore additional water treatment is required which is to be cost effective. Since standard primary and secondary treatment plants are unsuccessful at eliminating or degrading these harmful chemicals, a cost-effective tertiary treatment approach is proposed. Adsorption is a successful approach for Contaminants removal globally, because it is low installation expense, high performance and has easy operational design. Emerging pollutants have been removed from wastewaters using various adsorbents like activated carbons, improved bio chars, Nano adsorbents, hybrid adsorbents, and others. The purpose of this paper is to review the source of contaminants and the concept of adsorption when separating emerging contaminants. The present study aims to examine the adsorption mechanism as an effective approach for treating emerging contaminants. Then, the analysis of natural and man-made adsorbents for the separation of contaminants is examined along with its comparison. Also, future view on emerging contaminants and adsorbents in modern generation has been discussed.

Encapsulation of Highly Volatile Fragrances in Y Zeolites for Sustained Release: Experimental and Theoretical Studies

Volatility is an inherent fragrance attribute and typically implies a reduced perception over time. One possibility to elongate odor perception is utilizing controlled fragrance-delivery systems. Herein, the Y type of faujasite with different extra-framework cations (abbreviated as ZY, where Z represents Na+, Ca2+, or La3+) was examined as potential carriers for fragrance entrapment and delivery. d-Limonene (Lim) and linalool (Lol) as model fragrances were loaded in the pore space of Y zeolites, yielding composites FG@ZY (FG = Lim, Lol). It was found that the fragrance release profiles correlate highly with the cationic species located in the nonframework. The retention of fragrances in matrices increases in the order NaY < CaY < LaY for either limonene or linalool. Interestingly, the release rate of limonene was significantly slower than that of linalool when encapsulated in the same zeolite, although neat limonene has a much higher saturated vapor pressure than linalool. For instance, the total fraction of aroma released from Lim@LaY over 30 days was about 10%, while the value was ∼20% for Lol@LaY. Based on the density functional theory calculations, the above results could be well rationalized by the electrostatic attraction and shape selectivity of microporous matrices to the dopant molecules.

Incorporation of trivalent cations in NaX zeolite nanocrystals for the adsorption of O2 in the presence of CO2

The O₂ and CO₂ sorption properties of nanosized zeolite X with faujasite type structure through a partial ionic exchange of sodium (Na⁺) by trivalent cations (Gd³⁺ and Ce³⁺) were evaluated. Three faujasite samples were studied, the as-synthesized Na-X possessing Na⁺ solely, and the modified samples Na-Gd-X and Na-Ce-X containing Gd³⁺ (1.8 wt%) and Ce³⁺ (0.82 wt%), respectively. Incorporating scarce amounts of trivalent cations modified the adsorption affinity of zeolites towards O₂ and CO₂ as demonstrated by in situ Fourier-transform infrared spectroscopy (FTIR). While Na-Ce-X encounters the highest O₂ physisorption capacity, the Na-Gd-X is adsorbing the highest quantities of molecular CO₂. All three samples exhibit the chemisorbed CO₂ in the form of carbonates, while the Na-X stores carbonates in monodentate and polydentate forms, the Na-Gd-X and Na-Ce-X allow the formation of polydentate carbonates only. Density functional theory (DFT) calculations revealed that trivalent cations tend to adsorb gases through two cations simultaneously which explains the presence of polydentate carbonates exclusively in the corresponding modified zeolites. The DFT results confirmed the higher affinity of Na-Gd-X and Na-Ce-X nanocrystals towards O₂ in the presence of CO₂. The affinity of Na-Gd-X and Na-Ce-X nanocrystals towards O₂ opens the door of their use as oxygen transporters for medical applications where CO₂ is constantly present. The toxicity of the nanosized zeolites and their performance in O₂ release are reported too.

Veterinary utility of dried blood spots for detailed analysis of chlorinated pesticides and polychlorinated biphenyls by gas chromatography tandem mass spectrometry

Persistent organic pollutants (POPs) are organic compounds of anthropogenic origin that resist atmospheric and microbial degradation and thus persist in the environment and in food chains for exceptionally long periods of time. Veterinarians and wildlife researchers need simple methodologies for monitoring and measuring such compounds including two large and diverse categories, organochlorine pesticides (OCs) and polychlorinated biphenyls (PCBs), compounds that have been largely banned from production and use except for specific exceptions. We present development of methodologies for detection and quantitation of 22 OCs and 10 PCB congeners by tandem quadrupole gas chromatography-mass spectrometric analysis of Dried Blood Spots (DBS). Development was enabled by (1) optimization of suspension and extraction methodologies for DBS; (2) strategic streamlining and condensation of Multiple Reaction Monitoring (MRM) settings on GC/MS/MS; and (3) improvement of GC settings to accommodate all 32 compounds in a single chromatographic run per sample. The method was validated for parameters of linearity, limits of detection and quantitation, recovery and precision, and results from blood were shown to correlate well with those from DBS despite both being only 50 uL in volume. The method was applied successfully to blood samples from nine avian specimens submitted to the MSU Veterinary Diagnostic Lab, and all were shown to bear the burden of varying levels of OCs and/or PCB compounds.