hassan rezai

Today, due to the industrialization of societies, the existence of heavy metals has created many problems for humans, other organisms, and the environment. Lead (Pb) is highly toxic and the second most commonly used metal. The aim of this study was to evaluate the efficiency of melaminemodified nanographene oxide in the removal of Pb from aqueous media. To increase the efficiency of graphene oxide, it was mechanically converted to nano graphene oxide and melamine (4, 2 and 6-triazine, 3, 1 and 5 triamine). Experiments were performed at pH value of 3-8, temperature of 15-50°C, Pb concentration of 5-200 mg/g, adsorbent dose of 0.01-0.06 g, and contact time of 15- 150 minutes. The mechanism of the adsorption process was investigated using two Langmuir and Freundlich isotherm models, pseudo-first order and pseudo-second order kinetic equations, and thermodynamic equations. The results showed that the adsorption rate corresponds to the Freundlich isotherm model and pseudo-second order kinetic equation. Thermodynamic studies also showed that the adsorption process is associated with increasing irregularities and it is endothermic. In constant conditions (pH of 6, contact time of 60 minutes, ambient temperature of 22°C, Pb concentration of 20 mg/L, and adsorbent dose of 0.01 g), the adsorption capacity was 191.65 mg/g. The highest adsorption occurs at the concentration of 5 mg/L and the highest adsorption capacity and removal percentage was observed at a concentration of 200 mg/L, which were 1896.3 mg/g and 98.8%, respectively. Due to the high adsorption capacity, the adsorbent was able to remove lead from the contaminated environment.

The present study aimed to model the structural equations of expectations and educational services quality with students' satisfaction and loyalty emphasizing on mediating role of perceived value at Imam Khomeini International University in Qazvin. Based on the purpose this study is practical and in terms of data collection is descriptive survey. The statistical population consisted of 2996 undergraduate, postgraduate and Ph.D. students of International University. Stratified random sampling Commensurate with the size of the statistical society was done. For data gathering, expectations, educational service quality, perceived value, satisfaction and loyalty questionnaires were used. For reliability verification, the alpha coefficients were gained 0.78, 0.91, 0.85, 0.87 and 0.81 respectively which indicate the desirable reliability of tools. To assess the validity of the questionnaires, a confirmatory factor analysis was used and the validity of all questionnaires was confirmed. Finally 342 questionnaires were analyzed using SPSS and Lisrel software. According to descriptive tables and averages, the findings of this study showed that the university's status in the area of factors affecting student loyalty, which includes satisfaction, perceived value, level of meeting expectations, quality of educational services, is below average and not desirable. The findings of this study showed that the effect of expectations on educational service quality, students' perceived value, satisfaction and loyalty was positive and significant. The effect of educational service quality on perceived value wasn't significant. The effect of educational service quality on satisfaction and loyalty was positive and significant. The effect of perceived value on students' satisfaction and loyalty is positive and significant. These results emphasize the role of mediating role of perceived value in students' satisfaction and loyalty. In other words, improving the quality of educational services and satisfying the students' expectations, and consequently increasing the level of perceived value in students, is expected to increase their satisfaction and loyalty. Based on these results and considering the importance of perceived value, the conceptual model was presented.