Applicative Study(Part I):The Excellent Conditions to Remove in Batch Direct Textile Dyes(Direct Red,Direct Blue and Direct Yellow)from Aqueous Solutions by Adsorption Processes on Low-Cost Chitosan Films under Different Conditions

In recent years the development of chitosan (CH) based materials as useful adsorbent polymeric matrices is an expanding field in the area of adsorption science. Even though CH has been successfully used for dye removal from aqueous solutions due to its low cost, no considerations have been made about, for example, the effect of changing the pH of chitosan hydrogelor about the dehydrating effect of Ethanol (EtOH) treatment of chitosan film on the dyes removal from water. Consequently in our laboratory we carried out a study focusing the attention, mainly, on the potential use of CH films under different conditions, such as reducing the intrinsic pH, increasing the hydrophobic character by means of ethanol treatment and neutralization of CH films to improve their absorption power. Textile anionic dyes named Direct Red 83:1, Direct Yellow 86 and Direct Blue 78 have been studied with the aim of reducing the contact time of CH film in waste water improving the bleaching efficiency. Neutralized acid CH film and longtime dehydrated one result to be the better films in dye removal from water. Also the reduction of the CH solution acidity during the film preparation determines the decreasing of the contact time improving the results. The effect of initial dye concentration has been examined and the amount of dye adsorption in function of time t, qt (mg/cm2), for each analyzed film has been evaluated comparing the long term effect with the decoloration rate. A linear form of pseudo-first-order Lagergren model has been used and described. The best condition for removing all examined dyes from various dye solutions appears to be the dehydration of a novel projected CH film obtained by means of the film immersion in EtOH for 4 days. Also CH films prepared by well-known literature procedure and neutralized with NaOH treatment appear having an excellent behavior, however the film treatment requires a large quantity of water and time.

Degradation of Selected Indoor Air Pollutants:Comparison Study of Photocatalytic,Ozone-Assisted Photocatalytic and Amine Adsorption Processes

Indoor air pollutants impact human health,comfort and productivity.The method of photocatalysis has been applied mainly in flow reactors and little information is available on indoor air pollutant removal in airtight reactors.In the paper,experiments were carried out to remove formaldehyde(HCHO),ammonia(NH_3) and volatile organic compounds(VOCs)in the airtight and ventilated chambers.Results demonstrated that 90.4%of HCHO,92.3%of NH_3 and 57.9%of VOCs were removed in the amine adsorption process,while 67.5% (hereinbefore,these are the mass fraction)of HCHO,60.0%of NH_3,and 61.2%of VOCs were removed in the photocatalytic process.However,ozone-assisted photocatalytic process showed great potential to degrade indoor air pollutants in the ventilated chamber.Factors and mechanisms of the photocatalytic degradation of HCHO, NH_3 and VOCs were also discussed.

Nitrogen rejection from low quality natural gas by pressure swing adsorption experiments and simulation using dynamic adsorption isotherms

In order to remove N_(2) from low quality natural gas,a mathematical model has been established by Aspen adsorption,using the CH_(4)-selective sorbent silicalite-1 pellets.The dynamic adsorption isotherm was first simulated by breakthrough simulation of a CH_(4)/N_(2) mixture at different adsorption pressures and feed flow rates based on breakthrough experiments.The resulting simulated CH_(4) dynamic adsorption amounts were very close to the experimental data at three different adsorption pressures(100,200,and 300 kPa).Moreover,a single-bed,three-step pressure swing adsorption(PSA)experiment was performed,and the results were in good agreement with the simulated data,further corroborating the accuracy of the gas dynamic adsorption isotherm obtained by the simulation method.Finally,based on the simulated dynamic adsorption isotherm of CH_(4) and N_(2),a four-bed,eight-step PSA process has been designed,which enriched 75%(vol)CH_(4) and 80%(vol)CH_(4) to 95%(vol)and 99%(vol),and provided 99%(vol)recovery.

Effects of aging process on adsorption–desorption and bioavailability of fomesafen in an agricultural soil amended with rice hull biochar

Biochar has been introduced as an acceptable soil amendment due to its environmental benefits such as sequestering soil contaminants. However, the aging process in biochar amended soil probably decreases the adsorption capacity of biochar through changing its physico-chemical properties. Adsorption, leaching and bioavailability of fomesafen to corn in a Chinese soil amended by rice hull biochar after 0, 30, 90 and 180 days were investigated. Results showed that the addition of 0.5%-2% fresh biochar significantly increases the adsorption of fomesafen 4-26 times compare to unamended soil due to higher SSA of biochar. Biochar amendment also decreases fomesafen concentration in soil pore water by 5%-23% resulting lower risk of the herbicide for cultivated plants. However, the aging process decreased the adsorption capacity ofbiochar since the adsorption coefficient values which was 1.9-12.4 in 0.5%-2% fresh biochar amended soil, declined to 1.36-4.16, 1.13-2.78 and 0.95-2.31 in 1, 3 and 6-month aged treatments, respectively. Consequently, higher desorption, leaching and bioavailable fraction of fomesafen belonged to 6-month aged treatment. Nevertheless, rice hull biochar was effective for sequestering fomesafen as the adsorption capacity of biochar amended soil after 6 months of aging was still 2.5-5 times hi^her compared to that of unamended soil.

Mass transfer mechanisms in fixed-bed adsorption of erythromycin

The equilibrium and kinetic characteristics of the adsorption of erythromycin to Sepabeads SP825 were determined.The equilibrium data in a batch system was well described by a Langmuir isotherm.The separation performance was investigated in a fixed-bed system with respect to the adsorption superficial velocity,ionic strength and pH.A mathematical model was used to simulate the mass transfer mechanism,taking film mass transfer,pore diffusion and axial dispersion into account.The model predictions were consistent with the experi-mental data and were consequently used to determine the mass transfer coefficients.

MgO-based adsorbents for CO2 adsorption:Influence of structural and textural properties on the CO_2 adsorption performance

A series of MgO-based adsorbents were prepared through solution–combustion synthesis and ball-milling process.The prepared MgO-based powders were characterized using X-ray diffraction,scanning electron microscopy,N_2 physisorption measurements,and employed as potential adsorbents for CO_2 adsorption.The influence of structural and textural properties of these adsorbents over the CO_2 adsorption behaviour was also investigated.The results showed that MgO-based products prepared by solution–combustion and ball-milling processes,were highly porous,fluffy,nanocrystalline structures in nature,which are unique physico-chemical properties that significantly contribute to enhance their CO_2 adsorption.It was found that the MgO synthesized by solution combustion process,using a molar ratio of urea to magnesium nitrate（2：1）,and treated by ball-milling during 2.5 hr（MgO-BM2.5h）,exhibited the maximum CO_2 adsorption capacity of 1.611 mmol/g at 25℃ and 1 atm,mainly via chemisorption.The CO_2 adsorption behaviour on the MgO-based adsorbents was correlated to their improved specific surface area,total pore volume,pore size distribution and crystallinity.The reusability of synthesized MgO-BM2.5h was confirmed by five consecutive CO_2adsorption–desorption times,without any significant loss of performance,that supports the potential of MgO-based adsorbent.The results confirmed that the special features of MgO prepared by solution–combustion and treated by ball-milling during 2.5 hr are favorable to be used as effective MgO-based adsorbent in post-combustion CO_2 capture technologies.

Emerging contaminants as global environmental hazards.A bibliometric analysis

This paper presents a bibliometric analysis of peer-reviewed scientific literature on emerging contaminants published from 2000 through 2019.A total of 4968 documents(among research articles and review papers)collected from Scopus database were analyzed using the VOSviewer 1.6.11 software.According to our results,this topic has been capturing researchers’attention over the years and the latter five years of the analysis timespan corresponds to the period of highest scientific productivity on this subject,when a 70.4%of all analyzed documents were published.United States,China,Spain,Italy and Canada were the tope5 most productive countries in terms of number of published works,while Science of the Total Environment,Chemosphere,Environmental Science and Pollution Research,Environmental Pollution and Water Research stood out as the journals with the highest number of publications,gathering a 31%of papers and 34%of all citations.According to the frequency of author keywords,the main specific research topic assessed by the researchers are the occurrence of pharmaceuticals and personal care products in wastewater and the removal of such pollutants by the application of adsorption and advanced oxidation processes.