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The production of cobalt oxide nanoparticles and their use in the adsorption of methylene blue (MB) from solution is described in the paper. The X-ray diffraction patterns show that the synthesized cobalt oxide nanoparticles have a crystalline cubic structure. The study of the adsorption of methylene blue onto the cobalt oxide nanoparticles involved determining the contact time and initial concentration of the adsorption of MB on the adsorbent. The kinetics of adsorption were analyzed using two kinetic models (pseudo-first order and pseudo-second order), and the pseudo-second-order model was found to be the most appropriate for describing the behavior of the adsorption. This study indicates that the MLTS (monolayer with the same number of molecules per site) model is the most suitable model for describing methylene blue/cobalt oxide systems, and the parameter values help to further understand the adsorption process with the steric parameters. Indicating that methylene blue is horizontally adsorbed onto the surface of the cobalt oxide, which is bonded to two different receptor sites. Regarding the temperature effect, it was found that the adsorption capacity increased, with the experimental value ranging from 313.7 to 405.3 mg g−1, while the MLTS predicted 313.32 and 408.16 mg g−1. From the thermodynamic functions, high entropy was found around 280 mg L−1 concentration. For all concentrations and temperatures examined, the Gibbs free energy and enthalpy of adsorption were found to be negative and positive, respectively, suggesting that the system is spontaneous and endothermic. According to this study's findings, methylene blue adsorption onto cobalt oxide nanoparticles happens via the creation of a monolayer, in which the same amount of molecules are adsorbed at two distinct locations. The findings shed light on the methylene blue adsorption process onto cobalt oxide nanoparticles, which have a variety of uses, including the remediation of wastewater. [ABSTRACT FROM AUTHOR]

The promotion of the agricultural production constitutes a main challenge for Morocco. This goal often results in an increased use of pesticides and fertilizers compromising soils and waters. Moreover, in addition to large stocks of pesticides, the invasion by locusts from southern countries requiring massive use of insecticides remains a potential threat for Morocco. Consequently, a continuous monitoring of the different environmental compartments (soil, water, and air) is increasingly needed for all the Moroccan territory Owing to hundreds of soil and water samples to control, it is important to develop simple and inexpensive methods to assess pollution levels by pesticides in agricultural soils and neighboring waters. The sophisticated chromatographic methods, in spite of their high accuracy, are very expensive and hardly accessible; they can be reserved for laboratory accurate analyses and statutory inspections. The purpose of this research is to palliate to this issue by developing a spectrometric approach for monitoring soils and waters; an approach which is effective, fast, easy to implement and reliable. In this sense, fluorescence spectroscopy presents a high potential owing to its high sensitivity, ease and rapidity. Total excitation-emission (TEEMs) and total synchronous fluorescence (TSFMs) mappings make it possible to detect remains of fluorescent pesticides in soils or waters. The present investigation aims at the creation/extension of a total excitation-emission and total synchronous fluorescence mapping database to fingerprint those fluorescent pesticides in large use in Morocco. These fluorimetric fingerprints must allow the direct identification of any targeted fluorescent pesticide persisting in soil or water. After a large survey among farmers and agricultural product distributors, to target the best-selling and most used pesticides in different Moroccan regions, one hundred and five (105) pesticides have been fingerprinted. Applicability tests were carried out on the basis of field pre-surveys information and total fluorescence results. In the present work, the maps and synchronous spectra of a set of 57 commercial pesticides are reported. Moreover, four examples of TEEMs/TSFMs fingerprinting applications to recognize pesticide remains in soil samples are shown. The agricultural plantations monitored are located in the great agricultural region Doukkala at the western Atlantic side of Morocco. The catalogue has been enriched by a PCAbased statistical study to constitute groups of pesticides with similar spectrometric fingerprints. The emitting similarity inside pesticide groups, despite different active principles, was explained by similarity of formulation products. The implemented spectrofluorimetric approach is satisfying and seems suitable, at least, as a warning method in case of massive contamination of soils or waters. [ABSTRACT FROM AUTHOR]