Diamond Annual Review 2023/24

44 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 3 / 2 4 Cement may hold the key to chromium remediation Thepollutionofwaterwayswithhexavalent chromium(CR(VI)) is agrowing global problem due to historical and ongoing industrial processes, including tanning, textile preservation and chrome plating. If this polluted water is left untreated, it can affect freshwater drinking water supplies and, ultimately, the marine environment. One common remediation strategy is to reduce soluble Cr(VI) to the less harmful and insoluble Cr(III). The COPR is, however, extremely alkaline and, at high pH (11 and above), the effectiveness of traditional environmental reductants ( e.g. metallic Fe, Fe(II) and organic materials) is limited. Researchers from the University of Edinburgh are investigating a new method of remediation that would safely lock up hexavalent chromium so that it can be removed from the environment. The team created solutions with varying concentrations of potassium chromate (K 2 CrO4).Then, after adding tricalcium aluminate, they took samples of the resulting liquid and solid at various intervals. They used powder X-ray diffraction (PXRD) on Diamond’s I11 beamline to fully characterise the solid products. Their results showed that - in all concentrations - the amount of chromium in the solution reduced, and they could identify the chromium in the solid products. The team is currently conducting more experiments, moving towards more realistic conditions, and may soon be ready to test it on actual water samples from the Burn in Glasgow. Rae, R. et al. DOI: 10.1039/D2RA04497H Novel synthetic approach towards large-sized inorganic-organic hybrid glass Crystalline metal coordination compounds are a class of hybrid materials composed of metal ions coordinated to organic linkers, forming frameworks with various dimensionalities and functionalities. Several ofmetal coordination compounds can be vitrified to bulk samples. However, the vitrification of these materials is usually realised by the conventional melt-quenching technique, which typically needs special conditions ( e.g. , high temperatures and/or pressure, inert gas, or vacuum) to finally obtain small-sized glass samples.​ Researchers have developed a new synthetic technique, called “Crystallisation-Suppressing Approach”, by which the large-sized inorganic- organic hybrid glasses were fabricated at low temperature ( i.e. , 373 K) and under ambient conditions. In this technique, the crystallisation of two-dimensional (2D) zeolitic-imidazolate framework-7-III (ZIF-7-III) was suppressed by alcohol/acid solution, forming a supramolecular metal inorganic-organic complex (MIOC) glass with large-size and unique properties.​ By performing the X-ray Pair Distribution Function (PDF) analysis using Diamond’s I15-1 beamline and ultrahigh field 67Zn nuclear magnetic resonance measurements, the team revealed the local structure difference between the as-synthesised ZIF-7-III crystal and MIOC glass. The work is particularly important for the discovery and scale-up of new metal coordination compound glasses.​ Ali, M.A. et al. DOI: 10.1002/anie.202218094​ Crystallography Group Science Highlights Figure : (a)–(d) Powder X-ray diffraction patterns of the solid samples collected at various time points during the experiments (a) “0.2 M K 2 CrO 4 , (b) “0.1 M K 2 CrO 4 ”, (c) “0.02 M K 2 CrO 4 ”, and (d) “0.01 M K 2 CrO 4 ”. Figure: X-ray PDF data of the ZIF-7-III crystal and MIOC glass; Red sphere, O; pink, Zn; black, C; blue, N and grey, H.