Sorption Kinetics and Sequential Adsorption Analysis of Volatile Organic Compounds on Mesoporous Silica

Adsorption-desorption behaviors of polar and nonpolar volatile organic compounds (VOCs), namely, isopropanol and nonane, on mesoporous silica were studied using optical reflectance spectroscopy. Mesoporous silica was fabricated via electrochemical etching of silicon and subsequent thermal oxidation, resulting in an average pore diameter of 11 nm and a surface area of approximately 493 m²/g. The optical thickness of the porous layer, which is proportional to the number of adsorbed molecules, was measured using visible light reflectance interferometry. In situ adsorption and desorption kinetics were obtained for various mesoporous silica temperatures ranging from 10 to 70 °C. Sorption as a function of temperature was acquired for isopropanol and nonane. Sequential adsorption measurements of isopropanol and nonane were performed and showed that, when one VOC is introduced immediately following another, the second VOC displaces the first one regardless of the VOC's polarity and the strength of its interaction with the silica surface.

The unique features of non-competitive vs. competitive sorption: Tests against single volatile aromatic hydrocarbons and their quaternary mixtures

The adsorption characteristics of four aromatic hydrocarbons (i.e., benzene, toluene, xylene, and styrene) onto ground-activated carbon were investigated both independently and as a mixture of the four at <10 Pa partial pressures (e.g., 0-100 ppm concentration range). The maximum sorption capacities for benzene, toluene, styrene, and xylene were measured both as a sole component and as a mixture (at 10 Pa). In the former, the values were approximately 123, 184, 272, and 238 mg g^-1, respectively. In contrast, the latter values were 5, 52, 222, and 248 mg g^-1 respectively, showing dramatic reduction in lighter compounds (below C7) relative to heavier ones (above C8). The mechanistic detail of sorption has been explained in terms of Henry's law and Langmuir, Freundlich, Dubinin-Radushkevich, and Elovich isotherm models. The linearized Langmuir adsorption isotherm analysis showed three sorption pressure regions: low (<1 Pa, retrograde), intermediate (1-4 Pa), and high (4-10 Pa). As such, the outcome of this study offers a unique opportunity to acquire detailed information on the dramatic and dynamic effects of the sorptive interaction between competing sorbates, along with a common sorption process between sorbent and sorbate at 298 K.

The effect of diverse metal oxides in graphene composites on the adsorption isotherm of gaseous benzene

The effective removal technique is necessary for the real world treatment of a hazardous pollutant (e.g., gaseous benzene). In an effort to develop such technique, the adsorption efficiency of benzene in a nitrogen stream (5 Pa (50 ppm) at 50 mL atm min^-1 flow rate and 298 K) was assessed against 10 different metal oxide/GO composite materials (i.e., 1: graphene oxide Co (GO-Co (OH)₂), 2: graphene oxide Cu (GO-Cu(OH)₂), 3: graphene oxide Mn (GO-MnO), 4: graphene oxide Ni (GO-Ni(OH)₂), 5: graphene oxide Sn (GO-SnO₂), 6: reduced graphene oxide Co (rGO-Co(OH)₂), 7: reduced graphene oxide Cu (rGO-Cu(OH)₂), 8: reduced graphene oxide Mn (rGO-MnO), 9: reduced graphene oxide Ni (rGO-Ni(OH)₂), and 10: reduced graphene oxide Sn (rGO-SnO₂)) in reference to their pristine forms of graphene oxide (GO) and reduced graphene oxide (rGO). The highest adsorption capacities (at 100% breakthrough) were observed as ~23 mg g^-1 for both GO-Ni(OH)₂ and rGO-SnO₂, followed by GO (~19.1 mg g^-1) and GO-Co(OH)₂ (~18.8 mg g^-1). Therefore, the GO-Ni(OH)₂ and rGO-SnO₂ composites exhibited considerably high capacities to treat streams containing >5 Pa of benzene. However, the lowest adsorption capacity was found for GO-MnO (0.05 mg g^-1). Alternately, if expressed in terms of the 10% breakthrough volume (BTV), the five aforementioned materials showed values of 0.50, 0.46, 0.40, 0.44, and 0.39 L g^-1, respectively. The experimental data of target sorbents were fitted to linearized Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich isotherm models. Accordingly, the non-linear Langmuir isotherm model revealed the presence of two or more distinct sorption profiles for several of the tested sorbents. Most of the sorbents showed type-III isotherm profiles where the sorption capacity proportional to the loaded volume.

A comprehensive review on nano-molybdenum disulfide/DNA interfaces as emerging biosensing platforms

The development of nucleic acid-based portable platforms for the real-time analysis of diseases has attracted considerable scientific and commercial interest. Recently, 2D layered molybdenum sulfide (2D MoS₂ from here on) nanosheets have shown great potential for the development of next-generation platforms for efficient signal transduction. Through combination with DNA as a biorecognition medium, MoS₂ nanostructures have opened new opportunities to design and construct highly sensitive, specific, and commercially viable sensing devices. The use of specific short ssDNA sequences like aptamers has been proven to bind well with the unique transduction properties of 2D MoS₂ nanosheets to realize aptasensing devices. Such sensors can be operated on the principles of fluorescence, electro-cheumuluminescence, and electrochemistry with many advantageous features (e.g., robust biointerfacing through various conjugation chemistries, facile sensor assembly, high stability with regard to temperature/pH, and high affinity to target). This review encompasses the state of the art information on various design tactics and working principles of MoS₂/DNA sensor technology which is emerging as one of the most sought-after and valuable fields with the advent of nucleic acid inspired devices. To help achieve a new milestone in biosensing applications, great potential of this emerging technique is described further with regard to sensitivity, specificity, operational convenience, and versatility.

Self-assembled polymer vesicles in deciding action of Zn-sulfanilamide allergenicity

Allergic reactions to sulfonamide-based drugs are quite common; hence, medications containing sulfonamides are prescribed carefully. Metal ion complexation may block the nitrogen binding site of sulfonamide by complexation and reduce such responses. In this study, trace concentrations of Zn were found to bind with sulfanilamide at pH ∼ 1. The complexation was studied in water as well as in vesicular medium of polyethylene glycol (PEG) and a block copolymer, PPG-PEG-PPG. The binding constants (k) of Zn-sulfanilamide complex were determined in water, PEG, and PPG-PEG-PPG block copolymer media. The values suggest that complexation occurs best in water followed by PPG-PEG-PPG, PEG #4000, and PEG #12000. Though the binding constants are high in water and block copolymer media, the complex is not very stable as the absorbance value for the complex was found to decline with time. The same complex when prepared in polymer matrix shows higher stability. The results prompted us to explore the extraction possibilities of the Zn-sulfanilamide complex by using aqueous biphasic extraction systems comprising the polymers against sodium sulfate solution. The complex was analyzed for its allergenic response in different media by competitive enzyme-linked immunosorbent assay (ELISA) technique. The allergic response of the compounds in the respective media is the resultant of the binding constant and the stability of the complex in that particular medium.

Block copolymer as a novel functional phase in an aqueous biphasic system for species selective iodine extraction

This article describes a newly designed block copolymer based aqueous biphasic system (ABS, composed of two immiscible aqueous phases) which is further utilized to study extraction behavior of three iodine species viz., I₂, I⁻, and IO₄⁻.