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Natural organic matter (NOM) is present in all surface and ground waters and originates from degradation and by-products of living organisms and plants. NOM can be separated by HPLC-Organic Carbon Detection into five fractions: biopolymers, humic substances, building blocks, low molecular weight acids and low molecular weight neutrals. Water quality is affected by the presence of NOM (fractions) and moreover it can cause several issues during water treatment processes. Therefore, its removal by a variety of technologies is widely studied. Anion exchange resins (AER) can effectively remove a major part of this NOM, but due to its complex nature, the process is still not completely understood and optimized. In this work, the removal of NOM by macroporous styrenic weak (WBA), strong (SBA) and combined weak/strong (W/SBA) base anion exchange resins is studied. The resins were used in two industrial relevant counter ion forms: the OH- or free base form for SBA and WBA resins respectively, using an NaOH conditioning solution as applied in water demineralisation units and a Cl- form using NaCl for SBA resins and HCl for the WBA and W/SBA resins, as seen in drinking water treatment and Dupont’s recently developed weak basic NOM scavenger resins respectively. The effect of this conditioning on the equilibrium pH and driving forces for NOM removal in batch mode experiments using synthetic water containing model compounds for the different NOM fractions was investigated. This study demonstrated that next to AER resin selection, the conditioning procedure is an important parameter to be considered in the design of NOM removal processes, especially when specific NOM fractions are targeted.

Nanotechnology - defined as Key Enabling Technology in Europe - plays an important role in our society, e.g., in medicine, in sports, in water treatment applications, in energy devices and is now also emerging in the field of catalysis. It strongly encompasses research and development to synthesize, control, and manipulate catalytic systems of enhanced or even novel properties. These properties can be attributed to the size of the nanomaterial which is ranged in one or more external dimensions from approximately 1 to 100 nm.

Controlled drug release gained a sharply increasing interest over recent years. Multiple materials have been screened as possible drug carriers, ranging from biodegradable polymers to hydroxyapatite[1]. Periodic Mesoporous Organosilicas are valuable alternatives as they possess a high chemical and thermal stability combined with a biocompatible nature[2]. Furthermore, their large internal surface area permits a high drug loading. Careful selection of the organic ‘bridged’ functionality allows a controlled release with respect to external stimuli, such as pH or temperature, of the drugs which are adsorbed via weak and reversible interactions, e.g. H-bonding, ionic and hydrophobic-phobic interaction[3]. In this contribution a novel malonamide (MA-PMO) and a methyl-malonamide PMO (mMA-PMO) bearing a high amount of functionalities, capable of multiple intramolecular interactions, are developed and thoroughly characterized[4]. Subsequently, these hybrid materials are evaluated in the controlled drug release of Ibuprofen.

The efficient removal of organic pollutants from waste water is important to minimize their detrimental effects on the environment. Advanced adsorbent materials need to be developed to address this problem. Boron nitride (BN) has long been known for its high thermal and chemical stability. It is only recently that porous boron nitride is attracting attention as an adsorbent for pollutants [1,2]. The formation of BN-layers occurs which consist of a hexagonal plane with boron and nitrogen atoms linked by sp2 hybridized orbitals. This hexagonal BN is able to interact with organic pollutants via pi-pi interaction in a similar way as graphene layers interact with aromatic organic compounds. The effect of ceramization temperature on the material characteristics of porous BN was investigated as well as their capability to remove BPA from water.

(Trans)esterification reactions play a key role in today’s biorefineries. Conventionally, these reactions are performed using an acid and a base homogeneous catalyst, respectively for esterification and transesterification. Heterogeneous catalysis offers a competitive alternative for these reactions by not requiring dedicated catalyst separation and purification. A single, fixed bed catalytic reactor, comprising a top layer of acid catalyst for esterification of free fatty acids followed by a base catalyst bed for triglyceride transesterification, would allow intensifying present-day biorefinery conversion processes. In the present work, the attention is focused on the acid top layer, for which an acid ion-exchange resin has been considered. Apart from esterification, also acid catalyzed transesterification has been investigated on this resin. A fundamental kinetic model has been constructed to gain detailed insight in the (trans)esterification reactions that will be essential in the intensification of the corresponding biorefinery processes. Acid ion exchange resins have been selected as they are ecofriendly, noncorrosive and have a good stability and reusability. The investigated resin consists of a cross-linked polystyrene matrix with sulfonic acid groups as active sites. Due to its particular structure, the resin exhibits a remarkable swelling phenomenon when in contact with a polar solvent. Since an excess of methanol is used as (trans)esterification agent and water is formed by esterification, the resin is swollen during the reaction. The resin’s swelling determines the accessibility of its active sites and, hence, plays a critical role in the finally observed reaction kinetics. An experimental investigation of the temperature effect and that of the initial molar ratio of acetic acid and methanol for esterification and of ethyl acetate and methanol for transesterification, both catalyzed by Lewatit K1221, was performed. The experimental data have been adequately modelled using an Eley-Rideal reaction mechanism. Exchange between protonated methanol, which was assumed to, initially, occupy all active sites, and the acid or ester in esterification and transesterification, respectively, was explicitly accounted for. While the activation energy was determined at 49 kJ mol-1, irrespective of the reaction type, the difference in catalytic activity, is found back in the value for the rate coefficient, which is about 1 order of magnitude higher for esterification than for transesterification. A unique set of exchange coefficients was obtained, irrespective of the considered reaction, which indicates the model’s adequacy. Throughout the experimentation at 333 K and using an initial molar ratio 10:1, the catalyst’s active sites were found to be occupied by methanol for at least 60%.

The performance of a new ultra stable, regenerable adsorbent SH-ePMO for the removal of mercury from aqueous solutions was compared with that of a commercial ion exchange resin TP-214. The operating variables studied were initial mercury concentration and contact time. The adsorption isotherms showed favourable adsorption. The adsorption isotherms were analyzed using Langmuir and Freundlich models. The Langmuir model yielded the best fit for the SH-ePMO, whereas the Freundlich model fitted best the adsorption on TP-214. The maximum adsorption capacities were 66, resp. 456 mg/g for SH-ePMO, resp. TP-214. TP-214 is capable of purifying water to ppt-levels. The adsorption kinetics showed a fast adsorption for both adsorbents. The kinetics were analyzed using Lagergren’s pseudo-first-order and pseudo-second-order kinetic models. The pseudo-first-order kinetic model showed a good agreement of the experimental data of both adsorbents. This study clearly shows the potential of the ultra stable, regenerable SH-ePMO for removing mercury from aqueous solutions and confirms the performance of the ion exchanger resin TP-214.

A sustainable future for our world, with the help of renewable energy and green technologies... For a long time, this sounded like an idealism, a concept at best. But now, a little over 250 years since the first industrial revolution, it has become clear that all those decades of mindless resource consumption have left their mark on our planet. Sustainability is no longer a prestigious school project, but a dire necessity, at least if we want to keep our species alive for a few more centuries. However, as the Greek tragedian Euripides once said: “Nothing has more strength than dire necessity”, and thankfully the world is gradually shifting its views. We have developed and optimized technologies to help us achieve such a sustainable future. Electric cars, wind energy, solar and hydropower… The world is ready for its gradual shift towards clean energy, leaving fossil fuels behind. Sadly, the problems do no end there. While our intentions are noble this time, we have come to the realization that, in order to keep using these clean technologies, a sufficient supply of several important resources is required. Resources such as metals and other elements that are indispensable in the design and operation of ‘clean’ devices and machinery. As it turns out, some of these elements have become increasingly scarce over the past decades, up to a point where complete exhaustion is expected if we do not act in time. In this context, a group of metals, called the rare earths elements (REEs), play a central role. They are amongst the most critical elements in several sustainable technologies, whilst also being critical with respect to their (future) availability. It is shown throughout this work that it is difficult to mine them in a cost-effective way, and that a lot of geopolitics come into play to acquire them. Moreover, their recycling rate is disappointingly low, mainly because they are present in small quantities in their respective devices, and the current recycling technologies, in most cases, do not allow a cost-effective recovery. It is nonetheless of extreme importance that a steady REE supply is ensured, because in most cases these elements have no worthy replacements. In the domain of recycling, more and more interest is shown in the concept of urban mining, where the technosphere (i.e., electronic waste) serves as an actual mine, full of valuable resources. This ‘e-waste’ has the potential to supply a significant amount of rare earths to help satisfy an increasing demand. On the other hand, next to urban mining, improved (sustainable) primary mining should also be able to increase our REE supply. It is in this context that the core of this work resides. Both in primary REE mining and recycling processes, aqueous streams are often generated, containing varying fractions of these metals. It is shown that in the treatment of these solutions, a lot of improvement can be made in terms of applied technologies. While industrial techniques like solvent extraction will remain an obvious choice for highly concentrated solution processing (e.g., g/L scale), they prove to be cost-ineffective for more dilute streams (e.g., mg/L scale). In addition, when dealing with REE recycling or the processing of secondary deposits (e.g., resources with a typically lower REE content than primary ores), these techniques would face the similar issues. Therefore, adsorption technology is proposed in this work, as a worthy alternative. The advantages of this technique are discussed, and it is shown that adsorbents are ideal materials for low concentration recovery or removal or certain species of interest. With respect to REE mining and recovery, different domains are proposed where selective adsorption could earn its place as the prevailing technology, and the requirements for such adsorbents are discussed. Whether it is to recover rare earths from process or waste streams, or to purify REE-containing solutions from toxic elements (uranium, thorium…), adsorbents can be tailored readily towards a certain application. Further on, an introduction is given into the world of metal-organic frameworks (MOFs). The concept of using these versatile coordination polymers in aqueous environment as adsorbents is explored and documented with existing literature. The stability of MOFs will play a major role in their possible application as aqueous adsorbents. It was therefore investigated which structural parameters have a significant influence on this stability. In short words; What makes a MOF suitable for water-based applications? In addition, a study was performed on the long-term stability of several popular MOFs, regarding their behavior in different aqueous conditions, i.e., acidic, alkaline, oxidative... With this information a rational choice can be made in the selection of suitable MOFs for aqueous adsorption applications. This work then describes the application of a specific cage-type MOF, namely MIL-101(Cr), as a potential ideal support for aqueous adsorption. It was chosen based on its incredible stability, high porosity, and ready functionalizability. The MIL-101(Cr) was functionalized via two different routes with a specific ligand and its affinity for certain critical metals (REEs, uranium…) was investigated. In one approach, a carbamoylmethylphosphine oxide-type ligand (CMPO) was covalently anchored onto the surface of MIL-101 via a three-step method. Another approach encapsulates another CPMO-type ligand in-situ in the cages of MIL-101, where it is confined and cannot leach out. Both materials have been subjected to a comprehensive adsorption study, in which their performance in terms of selectivity, stability, uptake, kinetics, recyclability… is investigated. In conclusion, it is shown that several MOFs do possess the required characteristics to serve as aqueous-phase adsorbents. They can be tailored towards a specific application, via different functionalization methods. This was proven for the ultra-stable MIL-101(Cr), which could be functionalized with selective ligands for critical metals recovery. As there are several stable MOFs to explore, and various strategies to tailor them, it is safe to say that MOF-based adsorption opens up exciting avenues in the field of aqueous-phase metal recovery.

(Trans)esterification reactions with typical production volumes ranging from a few hundred to thousand tonnes per year are commercially important and are used to make esters which serve as precursors or additives for a variety of perfumes and flavours, pharmaceuticals, agrochemicals and polymers. The homogeneous Lewis or BrØnsted acids and bases that are commonly used for (trans)esterification purposes exhibit several well-known disadvantages, such as additional separation and neutralisation steps. A heterogeneously catalysed implementation of the reaction making use of acid ion exchange resins is promising as they are ecofriendly, noncorrosive and reusable. Acid ion exchange resins are promising catalysts for (trans)esterification. Thanks to their pronounced swelling when in contact with polar media, the highest conversions are obtained with a gel type resin, Lewatit K1221. The resins’ swelling significantly affects the catalytic activity and, hence, should also be reflected in the kinetic model. A novel kinetic model, implicitly accounting for resin swelling, was developed based on the following assumptions: (1) all active sites are occupied, (2) the exchange reactions between reagents or products are quasi equilibrated and (3) an Eley-Rideal type surface reaction between protonated (ester)acid with methanol from the bulk occurs as the rate-determining step. This kinetic model describes accurately the (trans)esterification reaction kinetics on different type of resins. Parameter estimates generally adopted physically meaningful values although the exchange coefficients obtained for acetic acid esterification indicated the need for further model refinement, in particular with respect to the description of the thermodynamics inside the resin. The kinetic model can be used as a helpful tool for resin selection. While resin selection and design frequently occurs on a trial and error base, the insight gained by the model, may provide clear guidelines about the desired resin properties. This knowledge may further lead to an enlargement of the use of ion exchange resins as catalysts, and, hence, also be exploited for industrial reactor design and optimization.