Adsorption of CO and NO molecules onto pentagonal clusters of aluminum: a DFT study.

DFT calculations were carried out in order to determine the electronic and structural properties of pentagonal Al n (I h and D 5d symmetries), Al n -CO, and Al n -NO clusters, where n = 7, 13, 19, 43, or 55 atoms. As n was increased, the bare clusters were found to exhibit a transition in electronic behavior (from semiconductor to conductor) at n = 43 atoms. Clusters with a bound CO or NO molecule also showed this behavior, although their HOMO-LUMO energy gaps were smaller than those for the corresponding bare clusters. As the size of the Al n -CO or Al n -NO cluster increased, the presence of extra p electrons improved the capacity of the cluster to adsorb a CO or NO molecule and resulted in an increase in the electronic charge directed from the aluminum atom at the adsorption site to the adsorbed species (CO or NO), thus strengthening the Al-CO or Al-NO bond. Furthermore, the Al n CO and Al n NO clusters with n = 43 and 55 exhibited chemisorption, as did the Al13-NO cluster; the other clusters presented physisorption, based on their adsorption energies. The tendency to adsorb either CO or NO increased with the size of the aluminum cluster. Graphical Abstract Adsorption of CO and NO molecules onto pentagonal clusters of aluminum: a DFT study.

Removal of textile dyes and metallic ions using polyelectrolytes and macroelectrolytes containing sulfonic acid groups.

This work reports the removal of textile dyes and metallic ions by means of adsorption and coagulation-flocculation using two polyelectrolytes and two macroelectrolytes containing sulfonic acid groups. The adsorption of textile dyes was studied in aqueous solutions containing cationic dyes and in wastewater containing a vat dye. Also, removal of vat and naphthol dyes was studied using the process of coagulation-flocculation. The results show these materials possess elevated adsorption capacity, and they accomplished removal rates above 97% in aqueous solutions. The removal of the vat dye improved the quality of the wastewater notably, and an uncolored effluent was obtained at the end of the treatment. The treatment using adsorption decreased the values for coloration, conductivity, suspended solids, and pH. The removal of vat and naphthol dyes by means of coagulation-flocculation was studied as well, and removal rates of 90% were obtained. The polyelectrolytes and macroelectrolytes also proved effective in the adsorption of metallic ions in wastewater. The treatment using adsorption accomplished high removal rates of metallic ions, and it showed greater selectivity towards Cu(2+), Fe(3+) and Pb(2+). A decrease in the content of solids as well as the values for COD and conductivity was observed in the wastewater as well. The analyses of FT-IR indicated that cationic dyes and metallic ions were chemisorbed by means of ionic exchange.

Textile dyes removal from aqueous solution using Opuntia ficus-indica fruit waste as adsorbent and its characterization.

For this research, three different adsorbents, one untreated and two chemically activated, were prepared from Opuntia ficus-indica fruit waste. By the construction of adsorption isotherms, its adsorption capabilities and the viability of its use in the removal of textile basic and direct type dyes were determined. It was found that the adsorbent with the most adsorption capacity for basic dyes was the one activated with NaClO, and, for direct dyes, it was the one activated with NaOH. Langmuir and Freundlich equations isotherms were applied for the analysis of the experimental data. It was found that the Freundlich model best described the adsorption behavior. The adsorption capacity was improved when the pH of the dye solution had an acid value. The specific surface area of the adsorbents was calculated by means of methylene blue adsorption at 298 K to stay within a range between 348 and 643 m(2) g(-1). The FTIR spectroscopic characterization technique, the SEM, the point of zero charge, and the elemental analysis show the chemical and physical characteristics of the studied adsorbents, which confirm the adsorption results obtained.

Removal of textile dyes from aqueous solutions by adsorption on biodegradable wastes.

The adsorption of the textile dyes Basic Blue 41, Aniline Blue, Reactive Black 5 and Mariposa Blue was studied from model solutions prepared in distilled water in the concentration range up to 2000 mg l(-1). Biodegradable wastes were used and are proposed here as adsorbents due to their abundance and inexpensiveness in the authors' country. The influence of the particle size, pH, presence of an electrolyte in the dye solution, adsorbent activation and competition in ternary dyes mixtures was determined in this study. Adsorption capacity of the adsorbents designated as HOMAP and POMAP with particle diameter less than 3 mm for the Basic Blue 41 dye was found to be 164 and 77 mg g(-1), respectively. The efficiency of the prepared adsorbents for removing basic, acid and reactive dyes with a concentration of 400 mg l(-1) was examined. A comparison of the adsorption capacity and desorption feasibility of the adsorbents was made. The basic dye was adsorbed with efficiencies varying from 87-98%, the reactive dye was removed in the range 60-98% and the add dye, 60-70% by three of the four adsorbents tested in this study. The determination of adsorption equilibrium concentrations was followed by HPLC with diode array detection.

Removal of metal ions from aqueous solution by adsorption on the natural adsorbent CACMM2.

The adsorption of Cd2+, Cr3+, Cu2+, Fe3+, Ni2+, Pb2+ and Zn2+ from aqueous solution was used to study the sorption properties of the adsorbent CACMM2 extracted from a cactus. Quantitation of the cation concentrations was performed by HPLC with diode array detection using on-column complex formation with 8-hydroxyquinoline. Removal degree from 100 mg M(n+) l(-1) solutions followed the series: Cu>Cd>Fe>Ni>Cr>Zn. Henry and Freundlich constants were determined since adsorption did not reach saturation plateaux in the studied concentration interval. Sorption of chromium by CACMM2 was stronger than the sorption onto lignin, calcium oxalate and cellulose up to 1,000 mg Cr3+ l(-1). Copper and iron were desorbed to a greater extent, while lead adsorption was practically irreversible. CACMM2 was able to remove more than 83% of chromate in a freshly prepared and exhausted chromate commercial solution.

Electrochemical treatment of textile dyes and their analysis by high-performance liquid chromatography with diode array detection.

Several textile dyes were individually exposed to electrochemical treatment. Chromaticity variation and the formation of degradation products were followed using a UV spectrophotometer and HPLC with diode array detection. Dyes studied belong to the azo (color index, C.I. 15,510), methine (C.I. 48,013), indigo (C.I. 73,040), natural (C.I. 75,760) and arylmethane (C.I. 42,000) classes. Aliquots of the solutions treated at constant potential were analyzed and compared with control dye solutions. The final electrolysis solutions obtained by using different electrode materials: Pt, Ti and diamond presented different chromatograms. It was found that the novel (in this application) diamond electrode is efficient in studying the degradation of various dyes. Possible fragmentation and molecule moiety rearrangement are proposed as a result of the electrochemical treatment.