Adsorption of Dye Molecules and Its Potential for the Development of Photoactive Hybrid Materials Based on Layered Silicates

Batch and column studies for the removal of basic red-46 dye and textile by using magnesium oxide (MgO), strontium titanium trioxide (SrTiO3), cobalt- and iron-doped lanthanum chromium trioxide (Co.Fe.LaCrO3), and cadmium sulfide (CdS)-doped graphene oxide nanocomposites

Despite efforts to reduce the risk of toxic chemicals, colors, and dyes being released into the environment from urban and industrial areas, there is still cause for concern. Colored water must be filtered and sterilized before it can be used for irrigation. The utilization of metal oxide and nanocomposite materials in wastewater treatment procedures appears to be a viable option for the future. Therefore, different compounds were doped with graphene oxide to identify the best material for dye removal by the adsorption process. According to recent studies, the ideal conditions for graphene oxide-doped magnesium oxide (GO/MgO) are as follows: pH 10 showed the highest adsorption capacity (qe) at 49.4 mg/g; an adsorbent dosage of 0.01 g/50 mL showed 48.3 mg/g qe; a shaking time of 30 min resulted in 44.2 mg/g qe; an initial dye concentration of 100 mg/L yielded 53.6 mg/g qe; and a temperature of 35 °C gave 49.5 mg/g qe. For graphene oxide-doped strontium titanate (GO/SrTiO3), the optimum conditions were as follows: pH 10 with 45.8 mg/g qe; an adsorbent dose of 0.01 g/50 mL with 40.5 mg/g qe; a shaking time of 30 min with 75 mg/g qe; and a temperature of 35 °C with 44.7 mg/g qe. Graphene oxide-doped cobalt and iron-doped lanthanum chromium titanate (GO/Co.Fe.LaCrO3) showed optimum conditions of pH 9 with 34.2 mg/g qe; an adsorbent dose of 0.01 g/50 mL with 27.5 mg/g qe; a shaking time of 45 min with 33.2 mg/g qe; an initial dye concentration of 100 mg/L with 37.6 mg/g qe; and a temperature of 35 °C with 42.5 mg/g qe. Graphene oxide-doped cadmium sulfide (GO/CdS) showed the following optimum conditions: pH 8 with 23.1 mg/g qe; an adsorbent dose of 0.01 g/50 mL with 25.5 mg/g qe; an initial dye concentration of 75 mg/L with 28.3 mg/g qe; and a temperature of 35 °C with 33.5 mg/g qe. The pseudo-first-order model was the best fit only for graphene oxide-doped magnesium oxide (GO/MgO) with an R2 value of 0.966, while the pseudo-second-order adsorption isotherm was the best fit for all four products, with R2 values ranging from 0.991 to 0.998. Additionally, the Langmuir adsorption isotherms provided good results for all four products, with R2 values ranging from 0.957 to 0.985. The Freundlich adsorption kinetics showed satisfactory fit only for graphene oxide-doped magnesium oxide (GO/MgO) and graphene oxide-doped cadmium sulfide (GO/CdS), with R2 values of 0.951 and 0.982, respectively. To examine the characteristics and practicality of the adsorption process, certain thermodynamic variables were calculated. The adsorption capability of the most efficient nanocomposites for the degradation of basic red-46 was significantly affected by various concentrations of heavy metal ions and electrolytes. In dye solutions containing surfactants/detergents, the adsorption efficiency of several effective photocatalysts for basic dyes was significantly reduced. A 0.5 M HCl solution was found to be the most effective for desorption. In column investigations, the optimal bed height, flow velocity, and dye intake levels were determined to be 3 cm, 1.8 mL/min, and 70 mg/L, respectively, for maximal adsorption of basic red-46. The adsorption investigation of genuine textile waste products has also been carried out to facilitate the practical deployment of this approach. The methods used in this study were cost-effective, easy to handle, and eco-friendly and involved no hazardous materials in the synthesis, making the resulting materials non-hazardous. All these methods were part of green chemistry.

Anti-Biofilm Effect of Hybrid Nanocomposite Functionalized with Erythrosine B on Staphylococcus aureus Due to Photodynamic Inactivation

Resistant biofilms formed by Staphylococcus aureus on medical devices pose a constant medical threat. A promising alternative to tackle this problem is photodynamic inactivation (PDI). This study focuses on a polyurethane (PU) material with an antimicrobial surface consisting of a composite based on silicate, polycation, and erythrosine B (EryB). The composite was characterized using X-ray diffraction and spectroscopy methods. Anti-biofilm effectiveness was determined after PDI by calculation of CFU mL-1. The liquid PU precursors penetrated a thin silicate film resulting in effective binding of the PU/silicate composite and the PU bulk phases. The incorporation of EryB into the composite matrix did not significantly alter the spectral properties or photoactivity of the dye. A green LED lamp and laser were used for PDI, while irradiation was performed for different periods. Preliminary experiments with EryB solutions on planktonic cells and biofilms optimized the conditions for PDI on the nanocomposite materials. Significant eradication of S. aureus biofilm on the composite surface was achieved by irradiation with an LED lamp and laser for 1.5 h and 10 min, respectively, resulting in a 10,000-fold reduction in biofilm growth. These results demonstrate potential for the development of antimicrobial polymer surfaces for modification of medical materials and devices.

Comprehensive analysis of cationic dye removal from synthetic and industrial wastewater using a semi-natural curcumin grafted biochar/poly acrylic acid composite hydrogel

Polymer composites offer a tailored framework as an exceptional candidate for water treatment due to their tunable chemical structure, porous 3D architecture, physiochemical stability, accessibility, pH-sensitivity and ease of use. In this study, curcumin-engineered biochar is embedded into a cross-linked polyacrylic acid hydrogel matrix using in situ polymerization for developing a semi-natural adsorbent for the removal of cationic dye from an aqueous solution. The physicochemical features of the generated composite hydrogel are significantly influenced by the implementation of curcumin-grafted biochar into the polyacrylic acid substrate. Comprehensive characteristic approaches were employed to explore all aspects of the adsorbent's properties, especially its removal efficacy. The methodical adsorption study was accomplished by monitoring dynamic factors such as pH, adsorbent content, time frame, and initial dye concentration. The presence of the porous aromatized structure of biochar, active oxygen-enrich functional groups (carboxyl, hydroxyl, keto, enol, ether) coupled with the conjugated curcumin structure facilitate the effective establishment of hydrogen bonds, electrostatic interactions, π-π interactions, electron donor-acceptor and charge-assisted H-bonding with the malachite green (MG) and rhodamine B (Rho) molecules. The highest adsorption capacities of MG and Rho reached 521 mg g-1 and 741 mg g-1 respectively, in the range of neutral pH, considering their molecular nature, functionalities, and unique adsorption mechanisms. The isothermal modeling was carried out with Henry, Langmuir, Jovanovic, Freundlich, Temkin, and Koble-Corrigan models to determine the adsorption system. Additionally, the kinetic data were assessed with Bangham, pseudo-first-order, pseudo-second-order, intra-particle, and liquid film diffusion models to ascertain the rate-limiting phase. The Koble-Corrigan and Langmuir isotherm models (R2 > 0.997) as well as pseudo-second-order (R2 > 0.998) and Elovich (R2 = 0.983 and 0.995) kinetics models provide a substantial level of concordance with empirical findings. The analysis of non-linear diffusion models revealed that the Bangham (R2 > 0.995) pore and liquid film diffusion (R2 > 0.960) models has major influence on the rate of the adsorption procedure. The binary adsorption test demonstrated higher efficacy of the synthesized adsorbent in the removal of malachite as compared to rhodamine. This study sheds light on the design of a cost-effective semi-natural polymeric composite for treating dye-polluted wastewaters, a major milestone toward environmental and ecological sustainability.

Exploiting the photophysical features of DMAN template in ITQ-51 zeotype in the search for FRET energy transfer

The combination between photoactive molecules and inorganic structures is of great interest for the development of advanced materials in the field of optics. Particularly, zeotypes with extra-large pore size are attractive because they allow the encapsulation of bulky dyes. The microporous aluminophoshate Mg-ITQ-51 (IFO-type structure) represents an ideal candidate because of the synergic combination of two crucial features: the IFO framework itself, which is composed of non-interconnected one-dimensional extra-large elliptical channels with a diameter up to 11 Å able to host bulky guest species, and the particular organic structure-directing agent used for the synthesis (1,8-bis(dimethylamino)naphthalene, DMAN), which efficiently fills the IFO pores, and is itself a photoactive molecule with interesting fluorescence properties in the blue range of the visible spectrum, thus providing a densely-incorporated donor species for FRET processes. Besides, occlusion of DMAN dye in the framework triggers a notable improvement of its fluorescence properties by confinement effect. To extend the action of the material and to mimic processes such as photosynthesis in which FRET is essential, two robust laser dyes with bulky size, rhodamine 123 and Nile Blue, have been encapsulated for the first time in a zeolitic framework, together with DMAN, in a straightforward one-pot synthesis. Thus, photoactive systems with emission in the entire visible range have been achieved due to a partial FRET between organic chromophores protected in a rigid aluminophosphate matrix.

Controversial Issues Related to Dye Adsorption on Clay Minerals: A Critical Review

This critical review points out the most serious and problematic issues to be found in the literature on the adsorption of dyes on clay minerals. The introduction draws attention to the fundamental problems, namely the insufficient characterization of adsorbents, the influence of impurities on the adsorption of dyes, and the choice of inappropriate models for the description of the very complex systems that clay minerals and their systems represent. This paper discusses the main processes accompanying adsorption in colloidal systems of clay minerals. The relationship between the stability of the colloidal systems and the adsorption of dye molecules is analyzed. The usual methodological procedures for determining and evaluating the adsorption of dyes are critically reviewed. A brief overview and examples of modified clay minerals and complex systems for the adsorption of organic dyes are summarized. This review is a guide for avoiding some faults in characterizing the adsorption of organic dyes on clay minerals, to improve the procedure for determining adsorption, to evaluate results correctly, and to find an appropriate theoretical interpretation. The main message of this article is a critical analysis of the current state of the research in this field, but at the same time, it is a guide on how to avoid the most common problems and mistakes.