Polarity and functionality tailored conjugated microporous polymer coatings on silica microspheres for enhanced pollutant adsorption.

Many sources of pollution that are generated by modern society are not addressable by conventional methods. Especially organic compounds, like pharmaceutics, are particularly hard to remove from waterbodies. Herein, a new approach is presented using conjugated microporous polymers (CMPs) to coat silica microparticles yielding specifically tailored adsorbents. The CMPs are generated with three different monomers: 2,6-dibromonaphthalene (DBN), 2,5-dibromoaniline (DBA) and 2,5-dibromopyridine (DBPN) respectively coupled to 1,3,5-triethynylbenzene (TEB) via Sonogashira coupling. By optimizing the polarity of the silica surface, all three CMPs were converted into microparticle coatings. The resulting hybrid materials feature the advantages of being adjustable in polarity and functionality, as well as morphology. Sedimentation allows facile removal of the coated microparticles after the adsorption. Further, the expansion of the CMP to a thin coating increases the accessible surface area compared to the bulk material. These effects were demonstrated by the adsorption of the model drug diclofenac. Thereby, the aniline-based CMP proved to be most advantageous due to a secondary crosslinking mechanism of amino and alkyne functionalities. An outstanding adsorption capacity of 228 mg diclofenac per gram of the aniline CMP within the hybrid material was achieved. This represents a five-fold increase compared to the value obtained by the pure CMP material underlining the advantages of the hybrid material.

SiO2 nanospheres as surfactant and template in aqueous dispersion polymerizations yielding highly nanoporous resin particles.

HYPOTHESIS: High nitrogen containing resins such as poly(melamine-co-formaldehyde) (PMF) are known for their very good adsorption properties. Until now, using an ecofriendly hard-templating approach with SiO2 nanospheres in water for synthesis, only yielded either highly porous particles with diameters up to 1 µm or non-porous particles with diameters above 1 µm. Small particles cannot be used as fixed bed adsorbents in columns because of the very high pressure occurring. EXPERIMENTS: To yield particles with high porosity and larger diameters for the use as fixed bed adsorbent, we investigated the influence of several synthesis parameters on porosity and particle morphology. FINDINGS: From all variations, we proposed a mechanism for the complex interplay between the PMF prepolymer and resin species with SiO2 nanoparticles acting both as Pickering-like surfactant and template particle. With this knowledge we were able to produce a suitable column material with high specific surface area up to 260 m2/g. We then proved the application of this material for aqueous dichromate adsorption in batch, yielding a maximum capacity of 138 mg/g with recyclability. In column experiments, the contamination of 5 mg/L dichromate in water was reduced to drinking water safe levels for an influent volume equal to over 160 bed volumes.

Tuning the pore structure of templated mesoporous poly(melamine-co-formaldehyde) particles toward diclofenac removal.

The increasing demand and implementation of pharmaceutics poses severe risk to different aquatic species as detectable contaminant in almost every surface water worldwide. Diclofenac (DCF) as one of the most common used analgesics was investigated as contaminant to be removed by adsorption onto nanoporous poly(melamine-co-formaldehyde) (PMF) particles featuring a very high amount of nitrogen functionalities. To achieve a high specific surface area (up to 416 m2/g) and a tunable pore system by hard templating, four different SiO2 nanoparticles were used as template. Differences in the pore formation and achieved pore structure were elucidated. For the first time, the adsorption of DCF onto PMF was tested. In batch adsorption experiments, impactful adsorption capacities as high as 76 µmol/g were achieved and complete removal at initial concentrations of 2 mg/L DCF. Differences in the connectivity and the micropore structure were decisive for uptake in low concentrations and the achieved adsorption capacity, respectively. As the presented PMF particles can be easily synthesized with the monomers formaldehyde and melamine combined with colloidal silica as sacrificial template and water as green solvent, this material presents a viable adsorbent for the removal of DCF at a larger scale. Our study further indicates a high potential for the removal of other pharmaceuticals.

Mesoporous Poly(melamine-co-formaldehyde) Particles for Efficient and Selective Phosphate and Sulfate Removal.

Due to the existence-threatening risk to aquatic life and entire ecosystems, the removal of oxyanions such as sulfate and phosphate from anthropogenic wastewaters, such as municipal effluents and acid mine drainage, is inevitable. Furthermore, phosphorus is an indispensable resource for worldwide plant fertilization, which cannot be replaced by any other substance. This raises phosphate to one of the most important mineral resources worldwide. Thus, efficient recovery of phosphate is essential for ecosystems and the economy. To face the harsh acidic conditions, such as for acid mine drainage, an adsorber material with a high chemical resistivity is beneficial. Poly(melamine-co-formaldehyde) (PMF) sustains these conditions whilst its very high amount of nitrogen functionalities (up to 53.7 wt.%) act as efficient adsorption sides. To increase adsorption capacities, PMF was synthesized in the form of mesoporous particles using a hard-templating approach yielding specific surface areas up to 409 m2/g. Different amounts of silica nanospheres were utilized as template and evaluated for the adsorption of sulfate and phosphate ions. The adsorption isotherms were validated by the Langmuir model. Due to their properties, the PMF particles possessed outperforming maximum adsorption capacities of 341 and 251 mg/g for phosphate and sulfate, respectively. Furthermore, selective adsorption of sulfate from mixed solutions of phosphate and sulfate was found for silica/PMF hybrid particles.

A Comparative Study on the Flocculation of Silica and China Clay with Chitosan and Synthetic Polyelectrolytes.

Flocculation is still one of the most important and efficient processes for water treatment. However, most industrial processes, such as in water treatment plants, still use huge amounts of synthetic polyelectrolytes for the flocculation process. Here we compare the flocculation of two different suspended particles, i.e., silica particles and china clay, with the biopolymer chitosan and two common strong synthetic polyelectrolytes. As a flocculant, chitosan featured a minimum uptake rate of 0.05 mg/g for silica and 1.8 mg/g for china clay. Polydiallyldimethylammonium chloride (PDADMAC) for comparison possessed a minimum uptake rate of 0.05 mg/g for silica and 2.2 mg/g for china clay. Chitosan as an environmentally friendly biopolymer competes with the synthetic polyelectrolytes and thus represents a beneficial economic alternative to synthetic flocculants.

Meso- and macroporous silica-based arsenic adsorbents: effect of pore size, nature of the active phase, and silicon release.

Arsenic pollution in ground and drinking water is a major problem worldwide due to the natural abundance of arsenic by dissolution from ground sediment or mining activities from anthropogenic activities. To overcome this issue, iron oxides as low-cost and non-toxic materials, have been widely studied as efficient adsorbents for arsenic removal, including when dispersed within porous silica supports. In this study, two head-to-head comparisons were developed to highlight the As(v)-adsorptive ability of meso- and macrostructured silica-based adsorbents. First, the role of the textural properties of a meso-(SBA15) and macrostructured (MOSF) silica support in affecting the structural-morphological features and the adsorption capacity of the active phase (Fe2O3) have been studied. Secondly, a comparison of the arsenic removal ability of inorganic (Fe2O3) and organic (amino groups) active phases was carried out on SBA15. Finally, since silica supports are commonly proposed for both environmental and biomedical applications as active phase carriers, we have investigated secondary silicon and iron pollution. The batch tests at different pH revealed better performance from both Fe2O3-composites at pH 3. The values of q m of 7.9 mg g-1 (53 mg gact -1) and 5.5 mg g-1 (37 mg gact -1) were obtained for SBA15 and MOSF, respectively (gact stands for mass of the active phase). The results suggest that mesostructured materials are more suitable for dispersing active phases as adsorbents for water treatment, due to the obtainment of very small Fe2O3 NPs (about 5 nm). Besides studying the influence of the pore size of SBA15 and MOSF on the adsorption process, the impact of the functionalization was analyzed on SBA15 as the most promising sample for As(v)-removal. The amino-functionalized SBA15 adsorbent (3-aminopropyltriethoxysilane, APTES) exhibited a q m of 12.4 mg g-1 and faster kinetics. Furthermore, issues associated with the release of iron and silicon during the sorption process, causing secondary pollution, were evaluated and critically discussed.