Green Chemistry Blog

Kai Leonhard and co-workers at the Univeristy of Stuttgart, Germany, provide an insight into the solvation mechanism of ionic liquids for cellulose dissolution using COSMO-RS combined with some other modelling studies. From the screening of more than 2200 ionic liquids, it is suggested that the anion as mainly responsible for the respective dissolving power. The German team also identified some new ionic liquids as potential candidates for cellulose dissolution. The results are in good qualitative agreement with those from the experimental data available in the literature.

Read the full article here: http://dx.doi.org/10.1039/c0gc00200c

A simple and easy way to make mixed zinc-cadmium sulfide materials that produce hydrogen by splitting water under visible light has been developed by scientists in the US and China. The mixed materials can harvest a wider range of wavelengths than conventional materials, making them more efficient. 

Photocatalytic conversion of sunlight to chemical energy, for example by producing hydrogen is an attractive alternative energy source and a feasible way to tackle the global energy and environmental pollution crises. Conventional photocatalysts, such as TiO₂, CdS or ZnS, possess excellent activity and stability but only absorb near-ultraviolet light – which accounts for only 4 per cent of the solar spectrum. Expensive noble metal co-catalysts, such as platinum can be added to increase their absorption range but this increases their cost. 

Now, Mietek Jaroniec from Kent State university, Ohio, and Jiaguo Yu from Wuhan University of Technology, have made mixed zinc-cadmium sulfide complexes doped with cadmium sulfide quantum dots (CdS QDs) that show high photocatalytic activity under visible light, without the need for noble metal additives. 

‘The high H₂-production activity of the CdS quantum dot-sensitised material under visible light can be attributed to the facilitated electron transfer from CdS QDs,’ says Jaroniec. The team made the mixed solid solution using a simple hydrothermal method to combine ZnS nanoparticles and Cd(NO₃)₂ salt. Followed by the thermodynamically favourable replacement of Zn²⁺ ions by Cd²⁺ ions using cation exchange. 

Quantitative analysis shows that the photocatalytic H₂-production of the new material is more than 50 times greater than CdS on its own, as well as being significantly better than platinum-doped ZnS under UV and visible light. 

Max Lu, an expert in clean energy and environmental technologies at the University of Queensland, Australia, says, ‘the results are quite exciting, and the CdS quantum dots are shown to be powerful in facilitating photocatalytic water splitting even without the use of Pt. If the stability is proven to be good, this system should offer opportunity to substantially lift the rate of hydrogen production under visible light irradiation.’ Next, the team plan to find other quantum dot-based materials, which could be used to enhance hydrogen generation. 

Jennifer Newton

You can read the full article online:

Preparation and enhanced visible-light photocatalytic H₂-production activity of CdS quantum dots-sensitized Zn_1-xCd_xS solid solution
Jiaguo Yu, Jun Zhang and Mietek Jaroniec, Green Chem., 2010
http://dx.doi.org/10.1039/c0gc00236d

A biorenewable polymer could replace synthetic plastic used in water bottles, claim US scientists. 

Polyethylene terephthalate (PET) is the third most common synthetic polymer behind polyethylene and polypropylene, with over 50 million metric tonnes of PET produced each year. Its unique thermal and physical properties make it ideal for use in industry, food packaging and soft drinks bottles. However, growing environmental concerns are causing a drive for more eco-friendly polymeric materials derived from biorenewable feedstocks to replace these petroleum-based plastics, but their properties have proved hard to mimic. 

PET is made up of alternating units of the fossil fuel feedstocks terephthalic acid and ethylene glycol, and it is this aromatic-aliphatic structure that is the key to its thermal stability. Now Stephen Miller at the University of Florida Gainesville in the US and colleagues have used lignin – one of the most abundant naturally occurring organic polymers – to produce a polymer that possesses alternating aromatic and aliphatic segments. Thus it not only bears a structural resemblance to PET but, importantly, it also has very similar thermal properties. 

Miller and co-workers combined acetic anhydride with vanillin – a by-product in the manufacture of paper from lignin – to form the monomer acetyldihydroferulic acid. Polymerisation of this monomer forms poly(dihydroferulic acid), PHFA, which mimics the structure and thermal properties of PET. Miller explains that ‘not only is the polymer designed to have a sustainable ‘green birth’, it is designed to have a ‘green death’ as it degrades into molecular units that resemble the building blocks of lignin itself.’ 

Geoffrey Coates, an expert on the design, synthesis and application of polymers, at Cornell University in Ithaca, US, comments ‘unlike some biorenewable polyesters that have poor thermal properties that limit their applications, this work focuses on materials that are comparable to PET. If other chemical and mechanical properties are suitable, and the economics of production are favourable, these polymers could have a promising future.’ 

In future, Miller’s team plan to investigate the long-term degradation characteristics of PHFA as well as performing scale-up fabrication studies to compare the biorenewable polymer with PET in different forms, such as a cup, plate or water bottle. 

Mary Badcock 

See full paper published in Green Chemistry

Biorenewable polyethylene terephthalate mimics derived from lignin and acetic acid
Laurent Mialon, Alexander G. Pemba and Stephen A. Miller, Green Chem., 2010, advanced article.