Among numerous methods developed in purification and separation industries, the adsorption process has received considerable attention due to its inexpensive, facile, and eco-friendly nature. The importance of the adsorption process causes extraordinary endeavors for modeling the adsorption isotherms during the years; thus, myriads of research have been conducted and many reviews have been published. In this paper, we have attempted to gather the most widely used adsorption isotherms and their related definitions, along with examples of correlated work of the recent decade. In the present review, 37 adsorption isotherms with about 400 references have been collected from the research published in the period of 2010-2020. The adsorption isotherms utilized are alphabetically organized for ease of access. The parameters of each isotherm, as well as the applicable definitions, are presented in the table, in addition to being discussed in the text. Another table is provided for the practical use of researchers, featuring the usage of the related isotherms in peer-reviewed studies.
In this study, a sustainable NH2-MIL-101(Al) is synthesized and subjected to characterization for cryogenic CO2 adsorption, isotherms, and thermodynamic study. The morphology revealed a highly porous surface. The XRD showed that NH2-MIL-101(Al) was crystalline. The NH2-MIL-101(Al) decomposes at a temperature (>500 °C) indicating excellent thermal stability. The BET investigation revealed the specific surface area of 2530 m2/g and the pore volume of 1.32 cm3/g. The CO2 adsorption capacity was found to be 9.55 wt% to 2.31 wt% within the investigated temperature range. The isotherms revealed the availability of adsorption sites with favorable adsorption at lower temperatures indicating the thermodynamically controlled process. The thermodynamics showed that the process is non-spontaneous, endothermic, with fewer disorders, chemisorption. Finally, the breakthrough time of NH2-MIL-101(Al) is 31.25% more than spherical glass beads. The CO2 captured by the particles was 2.29 kg m-3. The CO2 capture using glass packing was 121% less than NH2-MIL-101(Al) under similar conditions of temperature and pressure.
π-Acidic triangular silver(i) 3,5-bis(trifluoromethyl)pyrazolate (Ag3pz3) can form 1 : 1 adducts with dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (DMDBT), benzothiophene (BT), and 2,5-dimethylthiophene (DMT), which are stabilized by weak AgS and AgC contacts and sometimes by π-π stacking and, therefore, may represent a weak interaction model for some adsorptive desulfurization processes.
This work investigates the performances of coconut shell waste-based activated carbon (CSWAC) adsorption in batch studies for removal of ammoniacal nitrogen (NH3-N) and refractory pollutants (as indicated by decreasing COD concentration) from landfill leachate. To valorize unused resources, coconut shell, recovered and recycled from agricultural waste, was converted into activated carbon, which can be used for leachate treatment. The ozonation of the CSWAC was conducted to enhance its removal performance for target pollutants. The adsorption mechanisms of refractory pollutants by the adsorbent are proposed. Perspectives on nutrient recovery technologies from landfill leachate from the view-points of downstream processing are presented. Their removal efficiencies for both recalcitrant compounds and ammoniacal nitrogen were compared to those of other techniques reported in previous work. It is found that the ozonated CSWAC substantially removed COD (i.e. 76%) as well as NH3-N (i.e. 75%), as compared to the CSWAC without pretreatment (i.e. COD: 44%; NH3-N: 51%) with NH3-N and COD concentrations of 2750 and 8500 mg/L, respectively. This reveals the need of ozonation for the adsorbent to improve its performance for the removal of COD and NH3-N at optimized reactions: 30 g/L of CSWAC, pH 8, 200 rpm of shaking speed and 20 min of reaction time. Nevertheless, treatment of the leachate samples using the ozonated CSWAC alone was still unable to result in treated effluents that could meet the COD and NH3-N discharge standards below 200 and 5 mg/L, respectively, set by legislative requirements. This reveals that another treatment is necessary to be undertaken to comply with the requirement of their effluent limit.
A series of batch laboratory studies were conducted to investigate the suitability of activated carbon SA2 for the removal of cadmium ions and zinc ions from their aqueous solutions. The single component equilibrium data were analyzed using the Langmuir and Freundlich isotherms. Overall, the Langmuir isotherm showed a better fitting for all adsorptions under investigation in terms of correlation coefficient and error analysis (SSE only 18.2 for Cd2+ and 47.95 for Zn2+). As the binary adsorption is competitive, extended Langmuir models could not predict the binary component isotherm well. The modified extended Langmuir models were used to fit the binary system equilibrium data. The binary isotherm data could be described reasonably well by the modified
extended Langmuir model, as indicated in the error analysis.
The influence of biomass cellulosic content on biochar nanopore structure and adsorption capacity in aqueous phase was scarcely reported. Commercial cellulose (100% cellulose), oil palm frond (39.5% cellulose), and palm kernel shell (20.5% cellulose) were pyrolyzed AT 630 °C, characterized and tested for the adsorption of iodine and organic contaminants. The external surface area and average pore size increased with cellulosic content, where commercial cellulose formed biochar with external surface area of 95.4 m2/g and average pore size of 4.1 nm. The biochar from commercial cellulose had the largest adsorption capacities: 371.40 mg/g for iodine, 86.7 mg/L for tannic acid, 17.89 mg/g for COD and 60.35 mg/g for colour, while biochar from palm kernel shell had the least adsorption capacities. The cellulosic content reflected the differences in biochar nanopore structure and adsorption capacities, signifying the suitability of highly cellulosic biomass for producing biochar to effectively treat wastewater.
Microwave-steam activation (MSA), an innovative pyrolysis approach combining the use of microwave heating and steam activation, was investigated for its potential production of high grade activated carbon (AC) from waste palm shell (WPS) for methylene blue removal. MSA was performed via pyrolytic carbonization of WPS to produce biochar as the first step followed by steam activation of the biochar using microwave heating to form AC. Optimum yield and adsorption efficiency of methylene blue were obtained using response surface methodology involving several key process parameters. The resulting AC was characterized for its porous characteristics, surface morphology, proximate analysis and elemental compositions. MSA provided a high activation temperature above 500 °C with short process time of 15 min and rapid heating rate (≤150 °C/min). The results from optimization showed that one gram of AC produced from steam activation under 10 min of microwave heating at 550 °C can remove up to 38.5 mg of methylene blue. The AC showed a high and uniform surface porosity consisting high fixed carbon (73 wt%), micropore and BET surface area of 763.1 and 570.8 m2/g respectively, hence suggesting the great potential of MSA as a promising approach to produce high grade adsorbent for dye removal.
The emission of sulphur dioxide (SO2) gas from power plants and factories to the atmosphere has been an environmental challenge globally. Thus, there is a great interest to control the SO2 gas emission economically and effectively. This study aims to use and convert abundantly available oil palm fiber (OPF) biomass into an adsorbent to adsorb SO2 gas. The preparation of OPF biochar and activated biochar was optimised using the Response Surface Methodology (RSM) based on selected parameters (i.e., pyrolysis temperature, heating rate, holding time, activation temperature, activation time and CO2 flowrate). The best adsorbent was found to be the OPF activated biochar (OPFAB) compared to OPF biochar. OPFAB prepared at 753 °C for 73 min of activation time with 497 ml/min of CO2 flow yields the best adsorption capacity (33.09 mg/g) of SO2. Meanwhile, OPF pyrolysed at 450 °C of heating temperature, 12 °C/min of heating rate and 98 min of holding time yield adsorption capacity at 18.62 mg/g. Various characterisations were performed to investigate the properties and mechanism of the SO2 adsorption process. Thermal regeneration shows the possibilities for the spent adsorbent to be recycled. The findings imply OPFAB as a promising adsorbent for SO2 adsorption.
The suitability and efficacy of three-dimensional (3D) graphene, including its derivatives, have garnered widespread attention towards the development of novel, sustainable materials with ecological amenability. This is especially relevant towards its utilization as adsorbents of wastewater contaminants, such as heavy metals, dyes, and oil, which could be majorly attributed to its noteworthy physicochemical features, particularly elevated chemical and mechanical robustness, advanced permeability, as well as large specific surface area. In this review, we emphasize on the adsorptive elimination of oil particles from contaminated water. Specifically, we assess and collate recent literature on the conceptualization and designing stages of 3D graphene-based adsorbents (3DGBAs) towards oil adsorption, including their applications in either batch or continuous modes. In addition, we analytically evaluate the adsorption mechanism, including sorption sites, physical properties, surface chemistry of 3DGBA and interactions between the adsorbent and adsorbate involving the adsorptive removal of oil, as well as numerous effects of adsorption conditions on the adsorption performance, i.e. pH, temperature, initial concentration of oil contaminants and adsorbent dosage. Furthermore, we focus on the equilibrium isotherms and kinetic studies, in order to comprehend the oil elimination procedures. Lastly, we designate encouraging avenues and recommendations for a perpetual research thrust, and outline the associated future prospects and perspectives.
Over the past decade, there has been a surge of interest in using char (hydrochar or biochar) derived from biomass as persulfate (PS, either peroxymonosulfate or peroxydisulfate) activator for anthropogenic pollutants removal. While extensive investigation showed that char could be used as a PS activator, its sustainability over prolonged application is equivocal. This review provides an assessment of the knowledge gap related to the sustainability of char as a PS activator. The desirable char properties for PS activation are identified, include the high specific surface area and favorable surface chemistry. Various synthesis strategies to obtain the desirable properties during biomass pre-treatment, hydrochar and biochar synthesis, and char post-treatment are discussed. Thereafter, factors related to the sustainability of employing char as a PS activator for anthropogenic pollutants removal are critically evaluated. Among the critical factors include performance uncertainty, competing adsorption process, char stability during PS activation, biomass precursor variation, scalability, and toxic components in char. Finally, some potential research directions are provided. Fulfilling the sustainability factors will provide opportunity to employ char as an economical and efficient catalyst for sustainable environmental remediation.
The surfaces of NaY zeolite particles were modified by the alkylsilylation of n-octadecyltrichlorosilane (OTS). Two kinds of modified NaY zeolites were prepared; one with its external surface partially and the other fully covered with alkylsilyl groups. Since the size of OTS is bigger than the pore diameter of NaY, it is attached on the external surface, leaving the internal pore accessible to adsorbate molecules. As a result of alkylsilylation, the adsorption properties of these sorbents were improved. The adsorption properties of these materials were tested by their reaction in a mixture of paraquat and blue dye. The results demonstrate that the alkysilylated NaY materials are capable of simultaneous adsorption of paraquat and blue dye. Paraquat was selectively adsorbed into the internal pore of the zeolite whereas the dye on the externally attached alkylsilyl groups of the sorbent; displaying the unique bimodal amphiphilic character of the alkylsilylated NaY zeolites.
The importance of protein detection system for protein functions analyses in recent post-genomic era is rising with the emergence of label-free protein detection methods. We are focusing on a simple and practical label-free optical-detection method called anomalous reflection (AR) of gold. When a molecular layer forms on the gold surface, significant reduction in reflectivity can be observed at wavelengths of 400-500 nm. This allows the detection of molecular interactions by monitoring changes in reflectivity. In this chapter, we describe the AR method with three different application platforms: (1) gold, (2) gold containing alloy/composite (AuAg2O), and (3) metal-insulator-metal (MIM) thin layers. The AuAg2O composite and MIM are implemented as important concepts for signal enhancement process for the AR technique. Moreover, the observed molecular adsorption and activity is aided by a three-dimensional surface geometry, performed using poly(amidoamine) or PAMAM dendrimer modification. The described system is suitable to be used as a platform for high-throughput detection system in a chip format.
The current demands of sustainable green methodologies have increased the use of enzymatic technology in industrial processes. Employment of enzyme as biocatalysts offers the benefits of mild reaction conditions, biodegradability and catalytic efficiency. The harsh conditions of industrial processes, however, increase propensity of enzyme destabilization, shortening their industrial lifespan. Consequently, the technology of enzyme immobilization provides an effective means to circumvent these concerns by enhancing enzyme catalytic properties and also simplify downstream processing and improve operational stability. There are several techniques used to immobilize the enzymes onto supports which range from reversible physical adsorption and ionic linkages, to the irreversible stable covalent bonds. Such techniques produce immobilized enzymes of varying stability due to changes in the surface microenvironment and degree of multipoint attachment. Hence, it is mandatory to obtain information about the structure of the enzyme protein following interaction with the support surface as well as interactions of the enzymes with other proteins. Characterization technologies at the nanoscale level to study enzymes immobilized on surfaces are crucial to obtain valuable qualitative and quantitative information, including morphological visualization of the immobilized enzymes. These technologies are pertinent to assess efficacy of an immobilization technique and development of future enzyme immobilization strategies.
The importance of zeolite surface area and pore volume in adsorption processes has been much reported in literature. In addition to that, structural framework and pore network system may also influence the adsorption capacity and selectivity of methane on zeolite. This paper discusses the characteristics of methane adsorption based on several physical properties of the adsorbents such as surface area, pore volume, pore network system and its interaction with adsorbate. The study, using FTIR spectroscopy showed that the adsorbed methane at room temperature was detected in the FTIR region between 3200 cm–1 – 1200 cm–1. Based on the physical properties of the adsorbents and the FTIR spectra of adsorbed methane, the surface area was not the only factor that determined methane adsorption; in fact the type of pore network system of the adsorbent also affected the interaction, thus affecting the adsorption of methane in zeolite.
The present study sheds light on the physical and chemical characteristics of microcrystalline cellulose (MCC) isolated from oil palm fronds (OPF) pulps. It was found that the OPF MCC was identified as cellulose II polymorph, with higher crystallinity index than OPF α-cellulose (CrIOPFMCC: 71%>CrIOPFα-cellulose: 47%). This indicates that the acid hydrolysis allows the production of cellulose that is highly crystalline. BET surface area of OPF MCC was found to be higher than OPF α-cellulose (SBETOPFMCC: 5.64m(2)g(-1)>SBETOPFα-cellulose:Qa(0) 2.04m(2)g(-1)), which corroborates their potential as an adsorbent. In batch adsorption studies, it was observed that the experimental data fit well with Langmuir adsorption isotherm in comparison to Freundlich isotherm. The monolayer adsorption capacity (Qa(0)) of OPF MCC was found to be around 51.811mgg(-1) and the experimental data fitted well to pseudo-second-order kinetic model.
Urea removal is an important process in household wastewater purification and hemodialysis treatment. The efficiency of the urea removal can be improved by utilizing activated carbon fiber (ACF) for effective urea adsorption. In this study, ACF was prepared from oil palm empty fruit bunch (EFB) fiber via physicochemical activation using sulfuric acid as an activating reagent. Based on the FESEM result, ACF obtained after the carbonization and activation processes demonstrated uniform macropores with thick channel wall. ACF was found better prepared in 1.5:1 acid-to-EFB fiber ratio; where the pore size of ACF was analyzed as 1.2 nm in diameter with a predominant micropore volume of 0.39 cm(3) g(-1) and a BET surface area of 869 m(2) g(-1). The reaction kinetics of urea adsorption by the ACF was found to follow a pseudo-second order kinetic model. The equilibrium amount of urea adsorbed on ACF decreased from 877.907 to 134.098 mg g(-1) as the acid-to-fiber ratio increased from 0.75 to 4. During the adsorption process, the hydroxyl (OH) groups on ACF surface were ionized and became electronegatively charged due to the weak alkalinity of urea solution, causing ionic repulsion towards partially anionic urea. The ionic repulsion force between the electronegatively charged ACF surface and urea molecules became stronger when more OH functional groups appeared on ACF prepared at higher acid impregnation ratio. The results implied that EFB fiber based ACF can be used as an efficient adsorbent for the urea removal process.
A preliminary study was carried out to fabricate a three electrode system based on electrochemical sensoring. The cyclic voltammetry (CV) technique was chosen to select the type of metal suitable for evaporation and to compare the results produced from the fabricated gold electrode with the conventional macro-electrode system. The methodology and apparatus used involved low cost apparatus and methodology such as soft lithography, wet-etching, thermal evaporation, direct current sputtering, polymethylmethacrylate moulding and polydimethylsiloxane coating. The experiment was conducted at a fixed scan rate of 100 mV/s by using 0.01 M K3Fe(CN)6 in 0.1M KCl and well known method using Randles-Sevcik equation, peak current ratio and voltage separation was used to analyze the characterization on the fabricated sensors. Electrodes of 6.5 mm2 and 0.26 mm2 were fabricated to prove the adsorption effect of the reactant and the influence of the electrode area on the value of the peak current. CV analysis proved that the fabricated sensor was reliable for a range of 24 h at 25ºC room temperature.
A molecularly imprinted polymer (MIP), with the ability to bind Pb(II) ion, was prepared using the non-covalent molecular imprinting methods and evaluated as a sorbent for the Pb(II) ion uptake. 4-vinylbenzoic acid was chosen as the complexing monomer. The imprinted polymer was synthesized by radical polymerization. The template (Pb(II) ions) was removed using 0.1 M HCl. As a result, the efficient adsorption was found to occur at pH 7. The result also showed the applicability of the Langmuir model for the sorption, with the maximum sorption capacity of 204.08 μg/mg.
It is the first time to do investigation the reliability and validity of thirty kinetic and isotherm models for describing the behaviors of adsorption of silver nanoparticles (AgNPs) onto different adsorbents. The purpose of this study is therefore to assess the most reliable models for the adsorption of AgNPs onto feasibility of an adsorbent. The fifteen kinetic models and fifteen isotherm models were used to test secondary data of AgNPs adsorption collected from the various data sources. The rankings of arithmetic mean were estimated based on the six statistical analysis methods of using a dedicated software of the MATLAB Optimization Toolbox with a least square curve fitting function. The use of fractal-like mixed 1, 2-order model for describing the adsorption kinetics and that of Fritz-Schlunder and Baudu models for describing the adsorption isotherms can be recommended as the most reliable models for AgNPs adsorption onto the natural and synthetic adsorbent materials. The application of thirty models have been identified for the adsorption of AgNPs to clarify the usefulness of both groups of the kinetic and isotherm equations in the rank order of the levels of accuracy, and this significantly contributes to understandability and usability of the proper models and makes to knowledge beyond the existing literatures.