•This review covers the current progress of photocatalytic conversion of CO2 by inorganic photocatalysis.•A brief overview of some fundamental aspects for artificial photosynthesis has been ...given.•Several key factors for high-efficiency CO2 photoreduction are discussed.•The recent developments of photocatalytic reactors for artificial photosynthesis are highlighted.
Photocatalytic conversion of CO2 to either a renewable fuel or valuable chemicals, using solar energy has attracted more and more attention, due to the great potential to provide an alternative clean fuel and solve the problems related to the global warming. This review covers the current progress of photocatalytic conversion of CO2 by photocatalysis over the metal oxides. A brief overview of the fundamental aspects for artificial photosynthesis has been given and the development of novel photocatalysts for CO2 photoreduction has been discussed. Several key factors for high-efficiency CO2 photoreduction and the recent development of photocatalytic reactor design for this artificial photosynthesis have also been highlighted.
NiO and NiO–TiO2 nano-catalysts were synthetized using solution combustion synthesis (SCS) method and tested toward ammonia oxidation in synthetic and real wastewater. As-synthesized NiO ...nano-catalyst showed a tightly agglomerated nano-porous spherical structure with sizes ranging from 10 to 50 nm. NiO–TiO2 nano powders have homogenous structure with an average size of 19.5 ± 0.03 nm and a lattice spacing of 0.22 ± 0.03 nm corresponding to cubic planes of NiO and 0.25 ± 0.01 nm corresponding to TiO2. Cyclic voltammetry under alkaline condition at low potential ranging from 0.95 to 1.35 V vs. HgO/Hg improved the electro-chemical activity of the nano-catalysts by the formation of Ni(OH)2 film on the surface of catalyst as confirmed by XPS measurements. Ammonia electro-oxidation on nano-catalysts occurred at approximately 1.28 V vs. HgO/Hg and was highly pH-dependent. Ammonia removals up to 92.9 and 96.4% were achieved by NiO and NiO–TiO2, respectively. Total nitrogen material balance showed that the electro-chemical oxidation of ammonia produce small amounts of NO2− and NO3 and the balance N2. Ammonia oxidation at concentration less than 150 mM followed direct electron transfer mechanism, whereas at higher concentrations, the oxidation mechanism shifted to the indirect oxidation regime. Ammonia electro-oxidation kinetics followed zero order reaction at ammonia concentration ≤100 mM and first order kinetics at higher concentrations. More than 93% of ammonia, 35% of organic matter and 40% phosphorous were removed from real wastewater samples using electro-oxidation process confirming the suitability of this technology as advanced wastewater treatment.
•Electro-chemical activity of NiO improved by formation of Ni(OH)2 film at high pH.•Ammonia elctro-chemical oxidation produced les oxygenated species and the balance N2.•Synthesized nano-particles were activated toward ammonia oxidation in alkaline phase.•NiO and NiO–TiO2 nano-catalysts were used as advanced wastewater treatment technology.
The effect of initial concentration, particle size, mass of the adsorbent, pH and agitation speed on adsorption behaviour of methylene blue (MB) onto Jordanian diatomite has been investigated. The ...maximum adsorption capacity,
q, increased from 75 to 105
mg/g when pH of the dye solution increased from 4 to 11. It is clear that the ionisable charge sites on the diatomite surface increased when pH increased from 4 to 11. When the solution pH was above the pH
ZPC, the diatomite surface had a negative charge, while at low pH (pH
<
5.4) it has a positive charge. The adsorption capacity increased from 88.6 to 143.3
mg/g as the initial MB concentrations increased from 89.6 to 225.2
mg/dm
3. The experimental results were also applied to the pseudo-first and -second order kinetic models. It is noticed that the whole experimental data of MB adsorption onto diatomite did not follow the pseudo-first order model and had low correlation coefficients (
R
2
<
0.3). The calculated adsorption capacity,
q
e,
cal
, values obtained from pseudo-first order kinetic model did not give acceptable values,
q
e,
exp.
The maximum uptake capacity seems to be independent of the particle size of the diatomite when the particle size distribution is less than 250–500
μm. While at larger particle size 250–500
μm, the maximum uptake capacity was dependent on the particle size. It would imply that the MB adsorption is limited by the external surface and that intraparticle diffusion is reduced. The effect of the agitation speeds on the removal of MB from aqueous solution using the diatomite is quite low. The MB removal increased from 43 to 100% when mass of the diatomite increased from 0.3 to 1.7
g.
Abstract
The capture of CO
2
under high pressure and temperature is challenging and is required in a number for industrial applications including natural gas processing. In this work, we examine the ...use of benchmark hybrid ultraporous materials HUMs for their potential use in CO
2
adsorption processes under high-pressure conditions, with three varying temperatures (283, 298 and 318 K). NbOFFOVE-1-Ni and SIFSIX-3-Ni were the selected HUMs given their established superior CO
2
capacity under low pressure (0–1 bar). Both are microporous with highly ordered crystalline structures as compared to the mesoporous hexagonal silica (Santa Barbara Anhydrous-15 (SBA-15)). SBA-15 was previously tested for both low and high-pressure applications and can serve as a benchmark in this study. Sorbent characterization using XRD, SEM, FTIR and N
2
adsorption were conducted to assure the purity and structure of the sorbents. TGA analysis were conducted to establish the thermal stability of the sorbents under various temperatures. High-pressure CO
2
adsorption was conducted from 0–35 bar using magnetic suspension balance (Rubotherm). Although the SBA-15 had the highest surface (527 m
3
/g) are of the three adsorbents, the CO
2
adsorption capacity (0.42 mmol/g) was an order of magnitude less than the studies HUMs with SIFSIX-3-Ni having 2.6 mmol/g, NbOFFIVE-1-Ni achieving 2.5 mmol/g at 298 K. Multistage adsorption isotherms were obtained at different pressures. In addition, results indicate that electrostatics in HUMs are most effective at improving isosteric heat of adsorption
Q
st
and CO
2
uptake. Higher temperatures had negative effect on adsorption capacity for the HUMs and SBA-15 at pressures between 7–9 bar. In SAB-15 the effect of temperature is reversed in what is known as a cross over phenomena.
Temperature polarization is one of the major sources responsible for flux drop in membrane distillation systems due to the reduction in the driving force across the membrane. The present study offers ...a predictive model developed for the estimation of the temperature polarization coefficient across the membrane taking into consideration the simultaneous heat and mass transfer phenomena. The uniqueness of the developed model is its ability to predict the intermediate temperatures (temperatures along the flow path of the membrane sheet) which can be used to estimate the local flux and local temperature polarization coefficients as opposed to the methods used by others which estimate the TPC, using the average bulk temperatures, resulting in a tool that enables the estimation of the temperature polarization coefficient (TPC) at different operating conditions. It was found that higher feed temperatures result in higher temperature polarization effect and hence a lower TPC. It was also observed that TPC increases with feed flow rate. The highest TPC value of 0.82 was achieved for a flow rate of 3L/min and a feed–permeate temperature system of 60–20. The use of flow promoters further enhances the performance of the DCMD system and was reflected on increasing the TPC values (0.66 for a spacer filled channel compared to 0.47 for a spacer free operation) at 1.5L/min flow condition with 70–30 temperature system. The axially integrated local flux values predicted by the model were in good agreement with the experimentally measured fluxes.
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•Predictive DCMD model for the assessment of temperature polarization effect•Insight into local and global temperature polarization in DCMD•Model prediction of flux and temperature profiles in the axial direction of flow•Comparison of model predicted axially averaged flux and experimental flux•Accurate prediction of temperature profiles under a wide range of conditions
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•Ligand based nano-composite materials was fabricated for optical Cd(II) capturing.•The specific color was developed upon addition of Cd(II) ions at optimum condition.•Nano-composite ...material was highly selective and sensitive to Cd(II) ions.
In this study, a ligand was anchored with mesoporous silica, named as nano-composite materials, was applied in the detection and adsorption of cadmium (Cd(II)) ions from wastewater samples. The effects of solution pH, color optimization, limit of detection, contact time, initial concentration, ion selectivity and regeneration were systematically performed in the case of detection and adsorption operations. The solution pH was played an important factor both in the case of detection and adsorption, and the optimum pH were selected at 5.50 based on the high absorbance and adsorption ability. Upon addition of Cd(II) ions, the nano-composite materials was provided an excellent color, which was observed by the naked-eye. The detection limit was calculated to be 0.33 µg/L, which was lower than the permissible limit. Therefore, the Cd(II) ions was detected without using any sophisticated instruments. The equilibrium isotherm has been analyzed using Langmuir isotherm models, and the maximum adsorption capacity was 148.32 mg/g. The results clarified that the nano-composite material had the higher selectivity towards Cd(II) ions even in the presence of high concentration of divers metal ions. The material was reused in several cycles after elution operation with a suitable eluent of 0.25 M HCl. The nano-composite materials exhibited an excellent reusability because of its remarkable mechanical strength and highly efficient elution/regeneration operations ability. In the static treatment process, after seven cycles, Cd(II) ions was adsorbed efficiently and holding over 93% adsorption efficiency. The developed ligand functionalized nano-composite materials is quite simple and rapid with excellent repeatability for Cd(II) ions capturing and has a great potential for potential scale up for field application in real wastewater samples.
Since 2006, ceria is used as a redox reactive material for production of H2, CO, and syngas via a two-step solar driven thermochemical H2O/CO2 splitting cycle. Different forms of phase pure ceria ...were studied over a wide range of temperatures and oxygen partial pressures. To increase the redox reactivity and long-term stability, the effects of incorporation of different dopants in to the ceria fluorite structure (in varying proportions) were studied in detail. A variety of solar reactors, loaded with ceria based ceramics, were designed and developed to investigate the performance of these materials towards thermal reduction and H2O/CO2 splitting reactions. The thermodynamics and reaction kinetics of ceria based solar thermochemical H2O/CO2 splitting cycles were also explored heavily. This paper presents a detailed chronological insight into the development of ceria-based oxides as reactive materials for solar fuel production via thermochemical redox H2O/CO2 splitting cycles.
•The redox reactivity of the phase pure ceria can be improved by incorporating suitable dopants.•The current studies are directing towards utilization of reticulated porous ceria ceramics.•To improve the fuel yield, mass and heat transfer related to the redox reactions needs to be improved significantly.•Pilot scale design and development of ceria based solar reactors is essential to move towards commercialization.
This study investigates the impact of bio-carriers' surface area and shape, wastewater chemistry and operating temperature on ammonia removal from real wastewater effluents using Moving bed biofilm ...reactors (MBBRs) operated with three different AnoxKaldness bio-carriers (K3, K5, and M). The study concludes the surface area loading rate, specific surface area, and shape of bio-carrier affect ammonia removal under real conditions. MBBR kinetics and sensitivity for temperature changes were affected by bio-carrier type. High surface area bio-carriers resulted in low ammonia removal and bio-carrier clogging. Significant ammonia removals of 1.420 ± 0.06 and 1.103 ± 0.06 g − N/m2. d were achieved by K3(As = 500 m2/m3) at 35 and 20 °C, respectively. Lower removals were obtained by high surface area bio-carrier K5 (1.123 ± 0.06 and 0.920 ± 0.06 g − N/m2. d) and M (0.456 ± 0.05 and 0.295 ± 0.05 g − N/m2. d) at 35 and 20 °C, respectively. Theta model successfully represents ammonia removal kinetics with θ values of 1.12, 1.06 and 1.13 for bio-carrier K3, K5 and M respectively. MBBR technology is a feasible choice for treatment of real wastewater effluents containing high ammonia concentrations.
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•Ammonia a harmful constituent linked to acute/chronic toxicities in surface water•Impact of biocarriers' characteristics on ammonia removal by MMBR was evaluated.•MBBR technology is feasible choice to remove ammonia from Wastewater.•MBBR achieved effective removal of micronutrients at low temperatures.•Cold temperatures develop thick nitrifying biofilm, less cells and lower activity.
The continuous rise in the atmospheric concentration of carbon dioxide gas (CO2) is of significant global concern. Several methodologies and technologies are proposed and applied by the industries to ...mitigate the emissions of CO2 into the atmosphere. This review article offers a large number of studies that aim to capture, convert, or reduce CO2 by using a superb porous class of materials (metal-organic frameworks, MOFs), aiming to tackle this worldwide issue. MOFs possess several remarkable features ranging from high surface area and porosity to functionality and morphology. As a result of these unique features, MOFs were selected as the main class of porous material in this review article. MOFs act as an ideal candidate for the CO2 capture process. The main approaches for capturing CO2 are pre-combustion capture, post-combustion capture, and oxy-fuel combustion capture. The applications of MOFs in the carbon capture processes were extensively overviewed. In addition, the applications of MOFs in the adsorption, membrane separation, catalytic conversion, and electrochemical reduction processes of CO2 were also studied in order to provide new practical and efficient techniques for CO2 mitigation.
The catalytic conversion of CO2 to CO by the reverse water gas shift (RWGS) reaction followed by well-established synthesis gas conversion technologies could be a practical technique to convert CO2 ...to valuable chemicals and fuels in industrial settings. For catalyst developers, prevention of side reactions like methanation, low-temperature activity, and selectivity enhancements for the RWGS reaction are crucial concerns. Cerium oxide (ceria, CeO2) has received considerable attention in recent years due to its exceptional physical and chemical properties. This study reviews the use of ceria-supported active metal catalysts in RWGS reaction along with discussing some basic and fundamental features of ceria. The RWGS reaction mechanism, reaction kinetics on supported catalysts, as well as the importance of oxygen vacancies are also explored. Besides, recent advances in CeO2 supported metal catalyst design strategies for increasing CO2 conversion activity and selectivity towards CO are systematically identified, summarized, and assessed to understand the impacts of physicochemical parameters on catalytic performance such as morphologies, nanosize effects, compositions, promotional abilities, metal-support interactions (MSI) and the role of selected synthesis procedures for forming distinct structural morphologies. This brief review may help with future RWGS catalyst design and optimization.
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