Yes make sure to bookmark PowerShell Blogger | Everything powershell and more! and in regards to your question you cannot only search a specific folder. But since you are looking at only Sent Items just use this query which matches your requested 2012-09-28 through 2014-08-31
-SearchQuery {sent:09/28/2012..08/31/2014} -DeleteContent -Force which will remove it... or you can also just log it as you have in your example.