When I touch the emoji icon in text messaging the screen goes black and then back to the home page...

Did you already force restart the phone by holding the sleep and home button for about 10sec, until the Apple logo comes back on the screen again? You will not lose data, but this can cure some glitches.

If this does not help, setting the phone back to factory settings and restoring from the latest backup would be the next step. An encrypted backup made by iTunes will also contain your passwords for Wi-Fi and other accounts.

Restore your iPhone, iPad or iPod touch to factory settings

You'll have to create the encrypted backup prior to setting it back to factory settings.

Only a backup made by iTunes on the computer will include the Passwords, if you are backing up to iCloud, you'll have to fill in your passwords again manually the first time.