Removal Of Aqueous Pollutants Research Articles

Harnessing the Chemical Functionality of Metal-Organic Frameworks Toward Removal of Aqueous Pollutants.

Wastewater treatment has been bestowed with a plethora of materials; among them, metal-organic frameworks (MOFs) are one such kind with exceptional properties. Besides their application in gas adsorption and storage, they are applied in many fields. In orientation toward wastewater treatment, MOFs have been and are being successfully employed to capture a variety of aqueous pollutants, including both organic and inorganic ones. This review sheds light on the postsynthetic modifications (PSMs) performed over MOFs to adsorb and degrade recalcitrant. Modifications performed on the metal nodes and the linkers have been explained with reference to some widely used chemical modifications like alkylation, amination, thiol addition, tandem modifications, and coordinate modifications. The boost in pollutant removal efficacy, reaction rate, adsorption capacity, and selectivity for the modified MOFs is highlighted. The rationale and the robustness of micromotor MOFs, i.e., MOFs with motor activity, and their potential application in the capture of toxic pollutants are also presented for readers. This review also discusses the challenges and future recommendations to be considered in performing PSM over a MOF concerning wastewater treatment.

Synthesis of a Green Adsorbent Surface Gels: Development of Ratio Preparation of Polymer SA/Bentonite Bead, and its Industrial Applications for Removal of Aqueous Pollutants

In this research, polymer gels sodium alginate/bentonite clay adsorbent beads (SA/Ben) were prepared via encapsulating natural bentonite (Bn) in sodium alginate (SA). The ratio of Polymer Gels SA/Bn was used during preparation bead to yield beads (1/1 w/w), SA-Bn2 (1/2 w/w), and SA-Bn3 (1/3 w/w), respectively. These adsorbents were characterized via different characterisation FESEM, TEM, XRD and EDX to give high confidence of the prepared surface. The adsorption of Clonazepam drug (CLZ) from aqueous solution on the SA/Bn beads was investigated as a function of different factors, including the initial concentration of CLZ, the weight of SA/Bn beads gel, pH solution, temperature of solution and equilibrium time. Adsorption models of Langmuir and Freundlich isotherms were applied and were found to be well described via the isotherm of Freundlich model. The results showed that among the three types of prepared surfaces SA/Bn beads, SA-Bn1 presented the greatest CLZ adsorption capacity. Thermodynamic parameters were calculated including change free of Gibbs energy (ΔG), change entropy (ΔS), and change enthalpy. The change enthalpy of CLZ drug adsorption was found to be positive for the SA/Bn bead and the reaction of adsorption spontaneous and exothermic. After the adsorption proses the SA/Bn beads can easily be regenerated via water and re-used within four cycles.

Nanoconfinement-triggered oligomerization pathway for efficient removal of phenolic pollutants via a Fenton-like reaction

Heterogeneous Fenton reaction represents one of the most reliable technologies to ensure water safety, but is currently challenged by the sluggish Fe(III) reduction, excessive input of chemicals for organic mineralization, and undesirable carbon emission. Current endeavors to improve the catalytic performance of Fenton reaction are mostly focused on how to accelerate Fe(III) reduction, while the pollutant degradation step is habitually overlooked. Here, we report a nanoconfinement strategy by using graphene aerogel (GA) to support UiO-66-NH2-(Zr) binding atomic Fe(III), which alters the carbon transfer route during phenol removal from kinetically favored ring-opening route to thermodynamically favored oligomerization route. GA nanoconfinement favors the Fe(III) reduction by enriching the reductive intermediates and allows much faster phenol removal than the unconfined analog (by 208 times in terms of first-order rate constant) and highly efficient removal of total organic carbon, i.e., 92.2 ± 3.7% versus 3.6 ± 0.3% in 60 min. Moreover, this oligomerization route reduces the oxidant consumption for phenol removal by more than 95% and carbon emission by 77.9%, compared to the mineralization route in homogeneous Fe2++H2O2 system. Our findings may upgrade the regulatory toolkit for Fenton reactions and provide an alternative carbon transfer route for the removal of aqueous pollutants.

Nitrogen-doped porous carbon transformed from polymer carbon nitride for persulfate activation towards efficient degradation of tetracycline via the electron transfer-dominated non-radical pathway

BackgroundMetal-free carbon materials have been extensively researched for the removal of aqueous pollutants by persulfate activation. However, it was still worth exploring the contribution of adsorption of carbon materials to the catalytic efficiency as well as the ROS degradation pathway. MethodsA series of g-C3N4 and nitrogen-doped porous carbon materials were prepared by combining l-ascorbic acid with melamine-cyanuric acid (MCA) for the removal of tetracycline from wastewater. The carbon materials were analyzed by using XRD, XPS, Raman and other characterization methods. Furthermore, the effect of different reaction parameters on TC degradation was investigated, and the active species were identified by scavenging experiments and EPR. Significant findingsThe prepared porous carbon sample LAA-NC0.6 has a high nitrogen content of 31.93 at%. LAA-NC0.6 could completely remove TC within 40 min with first-order kinetic constant as high as 0.14995 min−1, which was 167-fold higher than that of pristine g-C3N4. Catalytic studies showed that the degradation of TC was a non-radical pathway dominated by electron transfer and that adsorption had a marked influence on the catalytic performance of the LAA-NC0.6/PS system.

Development of photocatalysis‐membrane separation reactor systems for aqueous pollutant removal

AbstractBackgroundIn our rapidly expanding society, the demand for clean water has steadily emerged as one of the most critical issues, promoting the development of numerous water treatment strategies.AimsCoupling photocatalysis and membrane separation technology provides an energy saving and environment‐friendly as well as sustainable method for aqueous pollutants removal due to the synergetic enhanced pollutant removal efficiency and improved anti‐fouling performance. It is of great scientific and technical significance to construct multifunctional photocatalysis‐membrane separation reactor systems (PMRs) with both the high photocatalytic activity and the strong stability.DiscussionHerein, in order to introduce the recent advances of this field, we present a critical review on developments of PMRs for aqueous pollutant removal, which includes photocatalysts and membranes, advanced methods for designing PMRs. Meanwhile, the recent applications of PMRs in aqueous pollutant removal, antifouling strategies, and mechanisms have also been summarized, including the latest development of PMRs coupling with other treatment methods. Furthermore, future perspective of PMRs is outlooked and predicted.ConclusionPMRs, designed for the removal of aqueous pollutants, offer a more promising solution for the sustainable development of our society in the future.

Photo-Fenton remediation of textile wastewater in fluidized-bed reactor using modified laterite: Hydrodynamic study and effect of operating parameters

There has been an increased interest for the use of naturally available catalysts in Fenton oxidation procedures. Nevertheless, the potential of laterite soil for the removal of aqueous pollutants via Fenton based technique has not been exhaustively explored. The fluidized bed photo Fenton approach was used in this study to treat textile wastewater with the goal of reducing total organic carbon (TOC) in the wastewater. Thermally modified laterite soil was used as a catalyst in the photo-Fenton process. Severalcharacterizationtechniques including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD) and X-ray photo-electron spectroscopy (XPS), were used to gain insight into the characteristics of a modified laterite catalyst. The application of this catalyst resulted in a significant reduction of total organic carbon (TOC) present in the textile wastewater. Specifically, a TOC reduction of 83% was observed after a reaction period of 100 min, at pH 3, 10 mm of bed height, 30 mM of H2O2 concentration, and a recirculating feed flow rate of 170 ml/min. Kinetic and hydrodynamic investigations were also carried out to have a better understanding of the catalytic processes occurring inside the fluidized-bed reactor. A first-order kinetics could potentially be used to explain the photo-degradation of textile effluent. Up to three successive oxidation cycles, laterite exhibited notable catalytic stability attributed to lesser surface site deactivation. A cost-benefit analysis of the fluidized bed photo-Fenton technique for treating textile effluent was also performed. The fluidized-bed Fenton approach may be a feasible option for treating wastewater containing different colours because of its low operating costs and low environmental effect.

One-step hydrothermal synthesis of rhombohedral ZnIn2S4 with high visible photocatalytic activity for aqueous pollutants removal

The phase composition of photocatalyst has a substantial effect on its photocatalytic activity. In this work, the rhombohedral phase ZnIn2S4 was synthesized by a one-step hydrothermal method by using inexpensive Na2S as a sulfur source with the assistance of NaCl. The Na2S as the S source can promote the generation of rhombohedral ZnIn2S4, and the addition of NaCl enhances the crystallinity of the as-prepared rhombohedral ZnIn2S4. The rhombohedral ZnIn2S4 nanosheets had a narrower energy gap, more negative conductive band potential, and higher separation efficiency of photogenerated carriers relative to the hexagonal ZnIn2S4. The as-synthesized rhombohedral ZnIn2S4 exhibited high visible photocatalytic activity with removal efficiencies of 96.7% in 80 min for the methyl orange, 86.3% in 120 min for ciprofloxacin hydrochloride and nearly 100% in 40 min for Cr(VI).

Adsorptive removal of aqueous pollutants on waste biomass-derived activated carbon: A mechanistic evaluation

The mismanagement of waste biomass is known to have environmental repercussions. Accordingly, valorisation of waste biomass holds significance. The present study evaluates valorisation of waste rice straw as waste biomass-derived activated carbon (WB-AC) as potential adsorbent for different aqueous pollutants. The WB-AC was characterized to have a distributed porous structure along with various surface functionalities. The WB-AC was utilized for adsorption of two different representative aqueous pollutants, namely iron (Fe) as metal and methylene blue (MB) as organic pollutants in the batch process. The effect of initial pollutants concentration, adsorbent dose, and adsorption temperature was studied under natural pH conditions. The adsorption of both pollutants (Fe and MB) was found to follow pseudo-second-order kinetics and was best described by the Langmuir isotherm model. The adsorption was noted as endothermic, spontaneous, and thermodynamically feasible. The physical interaction may be the dominant mechanism for both the pollutants; however ionic interaction seems predominant for Fe adsorption whereas chemical interaction might have also occurred alongside physical adsorption for MB. The maximum adsorption capacity of 172.41 mg g−1 and 95.24 mg g−1 were recorded for Fe and MB adsorption on WB-AC, respectively. A maximum of 99.56 % Fe removal and around 90.90 % MB removal were recorded in this study. Thus, WB-AC has been demonstrated as a universal adsorbent for different aqueous pollutants which include metals and organics.

Dehydrofluorination and One‐Pot Hydrothermal Process for Polyvinylidene fluoride/Polytetrafluoroethylene@TiO2 Membranes with Durable Superhydrophobicity toward Repeatable Separating and Photodegrading Oily Dyes in Water‐in‐Oil Emulsions

AbstractThe photocatalytic and inherently hydrophilic characteristic of titanium dioxide (TiO2) make it very suitable for separating oil‐in‐water emulsion and aqueous pollutants removal. However, the removal of the oily dyes in water‐in‐oil emulsion usually needs superhydrophobic/superoleophilic membranes. Although surface modification of TiO2 with fluorinated organic compounds can bring hydrophobicity, the hydrophobic surface would change back to a hydrophilic surface again after light illumination as fluorinated organic molecules are easily photodegraded too. To date, very few reports have successfully fabricated TiO2 photocatalysts keeping long‐term superhydrophobicity after repeatable photodegradation. Herein, an approach to fabricate polyvinylidene fluoride (PVDF)/polytetrafluoroethylene (PTFE) @TiO2 nanofibrous membranes through dehydrofluorination and one‐pot hydrothermal process, which possess stable superhydrophobicity in various harsh environments, is reported. For the first time, PTFE is bonded with PVDF through dehydrofluorination which induces crosslinking between PTFE and PVDF chains. Owing to the existence of PTFE, extensive hydrophobic TiO2 can be in situ grown on the rough surface of PVDF/PTFE nanofibers through one‐pot hydrothermal process. These features ensure that the membranes possess durable and high‐efficient water‐in‐oil emulsion separation and photodegradation performance. The photodegradation efficiency of the PVDF/PTFE@TiO2 membranes for oil‐soluble dyes remains above 95% even after ten cycles.

Separable and reactivated magnetic mZVAl/nFe3O4 composite induced by ball milling for efficient adsorption-reduction- sequestration of aqueous Cr(VI)

Destruction of the dense oxide layer on the surface of pristine or re-passivated micro zero-valent aluminum (mZVAl) can rejuvenated its reduction activity, which is beneficial to the removal of aqueous pollutants. To rejuvenated the reduction activity of mZVAl and rapidly recovery passivated mZVAl, in this study, a novel mZVAl/nFe3O4 composite with high activity and magnetic properties was synthesized by ball milling (BM). Compared with pristine mZVAl and nFe3O4, more than 95% of Cr(VI) could be removed in 30 min at 3.0 g/L mZVAl/nFe3O4 dosage over a wide range of pH (3.00–11.00). The removal of Cr(VI) conformed to the pseudo-first-order adsorption kinetic model, and the equilibrium adsorption data was in accordance with the Langmuir adsorption isotherm model. The maximum absorption (8.14 mg/g) was related to the BM parameters (the weight ratio of mZVAl/nFe3O4, BM speed and BM time). Accord to the effect of co-existing ions on the removal efficiency of Cr(VI), it was proved that the significance of the adsorption process was a prerequisite step for Cr(VI) reduction. Based on X-ray photoelectron spectroscopy (XPS) and the valence analysis of aqueous Cr, the Cr(VI) removal mechanism by mZVAl/nFe3O4 was also unraveled, in addition to achieving Cr(VI) reduction, also achieves the sequestration of total Cr under neutral environment. Furthermore, the reusability of mZVAl/nFe3O4 was limited by the accumulation of (hydr)oxide on its surface, but can be easily rejuvenated by BM again with a small amount of nFe3O4. In conclusion, mZVAl/nFe3O4 composite are a promising green material to reductive remove Cr(VI) from near-neutral wastewater.

Construction of Ag2CO3/BiOBr/CdS ternary composite photocatalyst with improved visible-light photocatalytic activity on tetracycline molecule degradation

Photocatalytic degradation was considered as a best strategy for the removal of antibiotic drug pollutants from wastewater. The photocatalyst of ABC (Ag2CO3/BiOBr/CdS) composite synthesized by hydrothermal and precipitation method. The ABC composite used to investigate the degradation activity of tetracycline (TC) under visible light irradiation. The physicochemical characterization methods (e.g. scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), ultraviolet visible spectroscopy (UV), photoluminescence (PL) and time resolved photoluminescence (TRPL) clearly indicate that the composite has been construct successfully that enhances the widened visible light absorption, induces charge transfer and separation efficiency of electron – hole pairs. The photocatalytic activity of all samples was examined through photodegradation of tetracycline in aqueous medium. The photocatalytic degradation rate of ABC catalyst could eliminate 98.79% of TC in 70 min, which is about 1.5 times that of Ag2CO3, 1.28 times that of BiOBr and 1.1 times that of BC catalyst, respectively. The role of operation parameters like, TC concentration, catalyst dosage and initial pH on TC degradation activity were studied. Quenching experiment was demonstrated that ·OH and O2·− were played a key role during the photocatalysis process that was evidently proved in electron paramagnetic resonance (EPR) experiment. In addition, the catalyst showed good activity perceived in reusability and stability test due to the synergistic effect between its components. The mechanism of degradation of TC in ABC composite was proposed based on the detailed analysis. The current study will give an efficient and recyclable photocatalyst for antibiotic aqueous pollutant removal.

Template-free synthesis of an eco-friendly flower-like Mg/Al/Fe-CLDH for efficient arsenate removal from aqueous solutions

• A novel flower-like Mg/Al/Fe-CLDH was synthesized for As(V) removal. • Mg/Al/Fe-CLDH exhibited excellent acid and alkali resistance and reusability. • The maximum adsorption capacity of the Mg/Al/Fe-CLDH was 70.7 mg/g. • As(V) ions intercalated into the interlayer region to reconstruct the hydrotalcite. Mg/Al-LDH is widely used in the removal of aqueous pollutants due to the large surface and high anion exchange capacity, but the traditional Mg/Al-LDH for arsenic removal has a narrow range of pH application. The present study focused on the modifying of the lamellar Mg/Al-LDH to synthesize flower-like nanoparticles for arsenate removal in a wide pH range. Results showed that Mg/Al/Fe-CLDH (calcined Mg/Al/Fe-LDH) exhibited an extremely high arsenate removal efficiency (e.g., reducing As(V) from 10 mg/L to 1 µg/L) in a wide pH range (2–12). Furthermore, it can keep excellent removal efficiency for arsenate under a complex anions environment (co-existing with CO 3 2− , SO 4 2− , PO 4 3− , and F − ), and maintain 80% removal efficiency for arsenate after 4 regeneration cycles. SEM, XRD, and XPS results unveiled the following enhancing mechanism for arsenate removal by using this modified Mg/Al-LDH: 1) partial content of ferric ions were successfully insert into the layers of Mg/Al-LDH and substituted by aluminium ions, which produce more affiliative sites for arsenate and expand its feasibility in a wide pH ranges; 2) the flower-like structures facilitate to offer more adsorption sites for arsenate due to its larger specific surface area. In brief, this flower-like Mg/Al/Fe-CLDH has great application potential for eco-friendly purity of arsenate from complicated industrial wastewater.

Investigation on synergistic effect of rGO and carbon quantum dots-embedded ZnO hollow spheres for improved photocatalytic aqueous pollutant removal process

Investigation on synergistic effect of rGO and carbon quantum dots-embedded ZnO hollow spheres for improved photocatalytic aqueous pollutant removal process

Rational design of novel 3D flower-like praseodymium molybdate anchored graphitic carbon Nitride: An efficient and sustainable photocatalyst for mitigation of carcinogenic pollutants

The rational design of heterostructured praseodymium molybdate@polymeric graphitic carbon nitride (Pr6MoO12@g-C3N4) was effectively designed by a new chemical strategy in a hydrothermal environment and followed by an ultrasound-assisted route. The features of the as-fabricated Pr6MoO12@g-C3N4 nanocomposite was broadly investigated by various standard characterization techniques like p-XRD,SEM, TEM, XPS, BET, PL,UV-DRS. The fabricated photocatalyst was demonstrated that high crystallinity and crystalline size was 46.7 nm. Furthermore, the 50 mg catalyst and 5 ppm (mg/L) of pollutant concentration were optimized conditions for the highest photocatalytic decomposition results. Interestingly, the Pr6MoO12@g-C3N4 composite synergistic photocatalytic abilities via excellent reusable stability towards the degradation of ciprofloxacin (CIP) and methyl parathion (MPT) as removal of aquatic pollutants. More distinctively, the Pr6MoO12@g-C3N4 nanocomposite was deliberate in the decolouration rate of CIP and MPT under visible light radiation: 98 % CIP and 97 % of MPT degradation in just 70 and 40 min respectively. A plausible charge separation/transfer pathway where redox species experiments implicate •OH is the most essential role while h + and O2•−contributed to a lesser extent in the catalytic process. This research work presented a versatile nature of the Pr6MoO12@g-C3N4 heterostructured material for energy harvesting and application in environmental crises.

In situ synthesis of novel peroxo-functionalized Ti3C2Tx adsorbent for aqueous pollutants removal: Role of oxygen-containing terminal groups

A novel peroxo-functionalized Ti3C2Tx adsorbent with abundant surface termination groups was facilely prepared in situ to remove aqueous anionic and cationic dyes. The adsorption behavior of methylene blue on peroxo-functionalized Ti3C2Tx was systematically investigated by adsorption kinetics, isotherms, and thermodynamics. Compared with Ti3C2Tx, the adsorption capacities of peroxo-functionalized Ti3C2Tx for cationic dyes methylene blue (558.0 mg g−1), rhodamine B (524.6 mg g−1) and anionic dyes methyl orange (292.6 mg g−1), congo red (258.2 mg g−1) were increased at room temperature without adjustment of pH, background ions and humic acid, etc of the contaminant solution by 7.9, 5.3, 5.9 and 4.6 times, respectively. In addition, peroxo-functionalized Ti3C2Tx could well tolerate the effects of pH, ionic strength, and humic acid. As revealed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, the adsorption mechanism of peroxo-functionalized Ti3C2Tx for anionic and cationic dyes was mainly attributed to the electrostatic interaction, hydrogen bonding interaction, and noncovalent surface-π attraction interaction. This study demonstrates a facile modification strategy for Ti3C2Tx adsorbent materials and aims to provide insights for the development of excellent Ti3C2Tx-based adsorbent materials.

Carbon Dots for Photocatalytic Degradation of Aqueous Pollutants: Recent Advancements

AbstractThe immense progress of humanity on the technological, domestic, and industrial fronts comes at the cost of polluting the planet. Aquatic pollution is particularly dangerous since all life forms are directly linked to it. Each year tons of industrial and domestic pollutants make their way into aqueous systems. Efficient removal/degradation of these pollutants is of prime importance for the sustainable future. Among many technologies, photodegradation is an emerging and promising method for the successful removal of aqueous pollutants since it is powered by abundant solar light. The last decade had shown that carbon dots are among the most promising materials that can be utilized as an efficient tool to derive various solar‐driven chemical reactions. Carbon dots possess unique photophysical and chemical properties such as light‐harvesting over a broad‐spectrum region, upconversion photoluminescence, photosensitizers, chemical inertness, and bivalent redox character, etc. The ease of synthesis of carbon dots at low cost also contributes hugely to their utilizations as an efficient photocatalyst for the degradation of aqueous pollutants. This review summarizes the recent progress made in the field of photodegradation of aqueous pollutants with the aid of carbon dots and their hybrids, highlighting the critical role carbon dots can play in the field.

Polyaniline-based adsorbents for aqueous pollutants removal: A review

• The advantages of polyaniline (PANI)-based adsorbents are discussed; • PANI-based adsorbents and their properties are summarized; • Adsorption mechanisms of PANI-based adsorbents are evaluated; • The future of pollutants removal by PANI-based adsorbents is viewed. Water contamination by a variety of pollutants, such as conventional pollutants (e.g. heavy metals and organics) and emerging micropollutants (e.g. personal care products and endocrine disrupting compounds) is of great concern. Various technologies have been developed to address this critical challenge. Among them, adsorption by polyaniline (PANI)-based nanocomposites, has gained growing research interest recently due to their unique electrical characteristics and many other benefits, such as facile synthesis, low cost, excellent environmental stability, simple acid-base doping/dedoping process, reactive NH– groups, and tunable properties. This paper provides a comprehensive review of the typical PANI-based adsorbents and their properties. Moreover, the removal of various aqueous contaminants (including heavy metals and metalloids, organic dyes and emerging pollutants) by PANI-based adsorbents is discussed and assessed. The unique doping/dedoping of PANI-based adsorbents alters the morphology, pore size, surface charge and functional groups of the adsorbents, leading to enhanced adsorbent-adsorbate interactions and thus adsorption performance. The adsorption mechanisms of aqueous pollutants by PANI-based adsorbents include electrostatic interactions, van der Waals forces, π–π interactions, hydrogen bonding, chelating and/or complexation effects. Finally, the future outlooks on aqueous pollutants removal by PANI-based adsorbents are presented.

Super-adsorptive and photo-regenerable carbon nanotube based membrane for highly efficient water purification

Carbon nanotube (CNT) based adsorbents have attracted extensive research interest for aqueous pollutants removal. However, such adsorbents face the problems of limited adsorption capacities and costly regeneration. Here, we report a highly adsorptive photo-regenerable CNT based multifunctional membrane with excellent self-cleaning properties via the facile vacuum filtration method, followed by FeOOH in-situ anchoring and silver-amino reaction. Various dyes (Rhodamine B, methylene blue, eosin Y and acid orange 7) and emerging contaminants (bisphenol A, amoxicillin and p-nitrophenol) were tested with the CNT based membrane. Our membrane exhibited superior adsorption performance to dyes among CNT based adsorbents reported in literature. In particular, the CNT based composite membrane displayed even better adsorption performance to cationic dyes. The adsorption capacities of the membrane for Rhodamine B and methylene blue were up to 181 and 247 mg/g, respectively. The membrane also had excellent self-cleaning and photo-regenerable properties after severe organic fouling. Our multifunctional CNT based membrane combined the features of adsorption, membrane separation, and catalytic degradation into one system, showing great promise for dye polluted wastewater purification. This study also offers a new strategy to engineer robust adsorptive, self-cleaning and regenerable membranes for wastewater treatment.

Hierarchical tannin-derived carbons as efficient tetracycline adsorbents

Mimosa tannin has been used to produce two different types of carbons materials: hydrothermal carbon (HTC) on the one hand, and ordered mesoporous carbon (OMC) on the other hand. Both were obtained after pyrolysis at 1173 K, resulting in materials with similar BET areas, close to 580 m2/g, but very different pore size distributions (PSDs). HTC was essentially microporous while OMC had a large fraction of mesopores. Tetracycline (TC) adsorption on these carbons was studied at equilibrium but kinetics experiments were also carried out at two different temperatures. The TC adsorption data were fitted by different mathematical, classical models, and new kinetic models were introduced to take into account their very different PSDs. While the two materials presented similar BET areas (ABET), the OMC had a TC adsorption capacity six times higher than that of the HTC. Adsorption kinetics were also strongly affected by the PSD. The importance of having high accessible pore volumes and not only high surface areas in order to have good performances in TC adsorption has been evidenced not only with our materials but also in the light of the TC adsorption data reported in the open literature. We proved that ABET, while easy to calculate and always reported, is not the best tool to assess the potential suitability of an adsorbent to the removal of aqueous pollutants.

A Facile Preparation of Ambient Pressure–Dried Hydrophilic Silica Aerogels and Their Application in Aqueous Dye Removal

Highly porous hydrophilic silica aerogels (SAs) are potential excellent adsorbents in aqueous media, which are generally synthesized via a standard sol–gel method followed by the relatively complex and dangerous supercritical fluid drying process. Herein, a facile and novel synthetic method applying ambient pressure drying technology for the rapid preparation of hydrophilic SAs is reported, which are soaked by metal cations without the need of traditional surface modification and supercritical fluid drying process. Chemical and physical properties of the hydrophilic SAs were characterized and compared with a trimethylchlorosilane (TMCS) modified hydrophobic silica aerogel. Besides the integrity and low shrinkage of the as-prepared products, Fourier transform infrared (FTIR) spectra and integrated thermal analyzer (ITA) results revealed the presence of hydroxyl groups as well as the absence of multitudinous hydrophobic groups on the silica surface after soaking. Field emission scanning electron microscope (FE-SEM) and Brunauer–Emmett–Teller (BET) measurements confirmed the mesopores inside the aerogel skeleton. Among the tested metal cations, the Mg2+ soaked SAs demonstrated the best pore properties (pore diameter 9.35 nm and pore volume 1.09 cc/g) while the Fe3+ soaked ones got the biggest surface area (855.62 m2/g) in contrast to other metal cations. Rhodamine B and Methylene blue solutions are used to check the absorption ability of the SAs in aqueous media, where the best adsorption capacity for Rhodamine B and Methylene blue reached 2.8 mg/g and 40.4 mg/g, respectively, showing a potential application in aqueous pollutant removal.