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CHEM0067: ADVANCED TOPICS IN ENVIRONMENTAL AND ENERGY MATERIALS

1.  Answer ALL parts. 1100 word limit.

(a) (i) Define hazard and risk in the context of a safety assessment. [2]

(ii) Calculate the E-factor and atom efficiency for the reaction below in which chromium sulfate and water are considered as by-products. Also calculate the E-factor assuming water can be recycled and is not a waste product.

3 PhCH(OH)CH₃ +2 CrO₃ +3 H₂SO₄ à  3 PhCOCH₃ + Cr₂(SO₄)₃ + 6 H₂O

Use the following relative atomic masses: C=12, H=1, O=16, S=32, Cr=52. [6]

(iii) What are the limitations of using the E-factor in terms of environmental impact? [3]

(b) (i) What is anaerobic digestion? Discuss the pros and cons of using anaerobic digestion as a way of creating biofuels. [7]

(ii) Describe the main features of a full ground source heat pump system that can heat a home and give a short explanation of how it works. Why is it able to harness energy from the ground? Why does it require electricity to operate? Once set up, why isn’t this more costly to run than a normal home gas boiler system? [7]

(iii) What are the key advantages of a ground source heat pump? (Do not repeat any points that have already been made in Q1b(ii)). [6]

(c) (i) Explain the steps in the decaffeination of coffee and how the properties of supercritical CO₂ are suitable for the process. [6]

(ii) If someone were to invent a way to cleanly generate and store hydrogen in a remote mountainous part of a developing country in South East Asia, discuss how this might improve the lives of local villages by relating your answer to at least four of the United Nations Sustainable Development Goals, UNSDGs, of your choice (do not use UNSDG 7).  [8]

2. Answer ALL parts. 1100 word limit.

(a) Compare and contrast different colloid stabilization mechanisms. These do not have to be specific chemical/material examples and can be conceptual. In your answer, consider what happens when neighbouring particles approach each other and how the surface stabilization contributes to colloid stability. Include diagrams in your answer. [14]

(b) The table below shows data collected from a dynamic light scattering instrument of four samples of nanoparticles with different surface stabilisers. The stabilisers were either citric acid, sodium phosphate, polyvinylpyrrolidone (molecular weight 10,000 g/mol) or poly(sodium 4-styrenesulfonate) (molecular weight 15,000 g/mol). From the data provided in the table, identify whether there is steric or electrostatic stabilization and justify your answer, commenting on the type of stabiliser which may be in use in the sample. Assume that the amount of stabiliser is the same for all samples, and that the measurement conditions are identical (room temperature, pH neutral buffer solution). [6]

(c) Comment on possible features of the colloidal particle suspension which  provided the dynamic light scattering graph illustrated below. Describe how data from the dynamic light scattering instrument could be used to provide more accurate information about the system. [3]

(d)  The research paper in appendix E2 investigates the extent to which microplastics have contributed to the burial of polycyclic aromatic hydrocarbons by sediments, compared to organic matter. In this paper, Liqi Zhang and Yuqiang Tao present a case study from an urban lake; Lake Quinhu. Answer all of the following questions, with reference to the article in appendix E2.

(i) Did the researchers find any correlation between the abundance of microplastics in the sediments of Lake Qianhu and annual plastic production in China in the period from 1975 to 2018? Discuss the results and account for any unexpected findings. [4]

(ii) Comment on the differences between the proportions of microplastics of various compositions in the period from 1975 to 1996 and those of the period from 1997 to 2018 in the sediments of Lake Qianhu. [4]

(iii) How do microplastics end up as sedimentation in an urban lake such as Lake Quinhu? Describe the journey of a plastic item, from synthesis to the lakebed. In your answer you should also consider the factors affecting transport and degradation of the polymer item. [14]

3. Answer ALL parts. 1100 word limit.

(a) The two research papers in appendix E3A and appendix E3B describe materials that have potential applications in carbon dioxide capture.  In both cases, the materials are based on the Metal-Organic Framework (MOF) known as MIL-101. In paper E3A, Y. Lin et al. describe an adsorbent material combining MIL-101 with polyethyleneimine (PEI). Paper E3B (Bahadori et al.) reports MIL-101 functionalised with ionic liquids. The resulting materials can act both as carbon capture materials and catalysts for CO₂ utilization.

(i) In MOFs, CO₂ adsorption can be enhanced by the presence of open metal sites. Briefly explain what is meant by open metal sites and how they can affect the material’s sorption behaviour. [3]

(ii) In paper E3A, the authors claim that, in general, the CO₂ absorption capacity of MOFs is unsatisfactory below 0.15 bar pressure of CO₂.  What is significant about a CO₂ pressure of 0.15 bar? Why might “most MOFs”  be ineffective at this pressure? [4]

(iii) Explain why the incorporation of PEI leads to improvements in both CO₂ absorption capacity below 0.15 bar, and CO₂/N₂ selectivity, compared to the original MIL-101. What other advantages do the PEI-MIL-101 materials possess? [6]

(iv) The MOF sample with the highest loading of PEI (PEI-MIL-101-125) has lower CO₂ capacity and selectivity at 25 °C, compared to the material with next highest loading, PEI-MIL-101-100 (table 1 and figure 5 in paper E3A), although in general these data improve with increasing PEI content, Suggest a reason for this decline in performance between the 100% and 125% PEI-loaded materials. [2]

(b) (i) Briefly explain what is meant by the term carbon dioxide utilization. What is the advantage of using molecules such as cyclic epoxides (as in paper E3B, scheme 1) in reactions with CO_2.  [3]

(ii) In paper E3B, the parent MOF is functionalized with an ionic liquid containing amino and imidazolium groups. Briefly explain why these particular functional groups are chosen in order to enhance CO₂ uptake. [2]

(iii) Two different synthetic approaches are used, leading to the materials MIL-IL(A) and MIL-IL(B).  Explain the difference between the two functionalised MOFs in terms of the structure of the materials, and suggest reasons why MIL-IL(B) has the higher porosity and measured CO₂ capacity, compared to MIL-IL(A) [e.g. see figures 6 and 7(1) in paper E3B]. [6]

(iv) Paper E3B demonstrates the use of MIL-IL(A) and MIL-IL(B) as catalysts for the cycloaddition of CO₂ to epoxides. What is the main advantage of MIL-IL(B) over MIL-IL(A) as a catalyst?  Considering the conditions required for the cycloaddition reactions compared to CO₂ capture, comment on the practicalities of using material MIL-IL(B) for CO₂ capture and utilization. [4]

(c) Discuss whether further research into polymer- or ionic liquid-functionalised MOFs for carbon capture and/or utilization would be a worthwhile use of public funding.  You may wish to distinguish between the materials in papers E3A and E3B, to compare with at least one other material discussed during the course, and to consider some of the following questions in your answer:

· How effective and resilient are these materials compared to other CO₂ capture materials, or CO₂ conversion catalysts?

· Are there other environmental, or “green” benefits in using these materials?  

· Are there further data, not provided by the authors, that would be useful to obtain?

· Are there clear strategies which could be developed and refined by further research?

· Are there more pro mising avenues of research that could be followed instead?   [15]